Table of Contents
Not-Lola's Guide to Basic Magic Use
This guide has been adapted from the original Steam Community post, with some edits for factual accuracy to Dominions 5, to make the hoverlinks work and for stylistic consistency.
Introduction
Dominions is filled with many spells, most of which are - at best - extremely niche. Many are quickly obsoleted for all but the most recondite purposes, some just sort of suck even when you get access to them, or are useful in circumstances more easily solved with other spells… in the same path.
However which spells are useful and which aren't is not immediately obvious, especially in battles that are confusing swirls of units and glittery particle effects.
This guide is a list of spells that are, in general, pretty good. Spells you can cast and in most situations they'll help you out.
- Situational spells are in italics.
- Spells that are nearly always good are in bold.
- Spells that are still good but not as omnipurpose as bolded spells, but still less situational than italic spells, are just in regular, good ol' plaintext.
- Some spells are bolded and italicized, because I think they are situational but v. strong in that situation.
Higher research spells (level 7+) will often not be mentioned or be mentioned only in passing. Lategame dominions is its own thing, and this guide is aimed at newer players.
Terminology is used in this guide sometimes, translations of which can hopefully be found here. If you wish to look up the spells, Larz' Inspector allows you to do so via the 'spells' tab.
Earth
Earth has some of the strongest buffs in the game, in addition to a variety of useful spells. It is less good under certain circumstances vs specific kinds of targets but it has quite a variety of broadly applicable tactics.
Combat Spells
Earth Meld
- Stops enemies for a turn no matter how strong they are, breaks formations, ties down elves, doesn't work on flying foes.
- Is bold due to coming online early and having a good aoe, falls off to plaintext later
Marble Warriors
- Makes troops basically immune to mundane weapon attacks and a variety of damaging spells in a huge aoe, possibly the strongest spell in the entire game
Summon Earth Elemental
- Note this isn't the 'lesser' version, it summons a size 6 trampler with a lot of hp and multiple forms
- Trample does immense damage and while size 6 things can block it from trampling, they are rare.
- They do a lot better with troop support or in great numbers, alone they can be swarmed down
Iron Warriors
- Used as a buff for thugs, super-elites (such as Wights or Elephants), or elementals (which requires good timing)
- Extremely strong in that niche.
Strength of Giants
- High aoe, good early buff, usually worth painting on your troops if you have it.
- Only not bold because +4 str scales less than +15 base protection.
Legions of Steel
- High aoe, good early buff, usually worth painting on your troops if you have it.
- Only not bold because +3 armour prot scales less than +15 base protection,
Maws of the Earth
- High damage attack spell that also Earth Melds, requires a gem, has range issues, and isn't as powerful as buffs
- Despite all that, it's one of the stronger damage spells in the game due to no projectile, decent precision, armour piercing damage, good aoe, and secondary effect.
Earthquake
- As it is one of the few options in the game to do instant, non elemental battlefield wide damage it is very strong in that role - but that role is only useful sometimes.
Weapons of Sharpness
- Hard to cast but good AoE. One of the few counters to prot-stacking. Makes things die. Does not counter chump blocking (skeletons/bugs) or powerful evo attacks (that kill faster than melee attacks do).
- A key buff for elite troops designed to actually kill things in melee. Combos well with Mass Flight.
Gifts from Heaven
- Crosspath
3
1, drops an immense damage meteor on the field. I say 'the field' because they are slow, they miss, and they go everywhere. With prec boosting, is one of the few spells to delete tanky sacreds without any conditional things (like resists or MR negating).
Globals
Earth Blood Deep Well
- Generates
gems. Very little in E is gem-cheap, given how much of it you generally want to deploy. Casting even just Marble Warriors with every group and army you want to cast it on can drain your entire income very easily, and you often want Earth Boots for guys as well.
Items
Earth Boots
- Very cheap, very useful, often enables the vast majority of your earth buffs from even such humble beginnings as1. One of the most common, if not the most common, booster item used in the game.
Fire
Fire is mostly good for some specific applications - research boosters, chaff/skeleton clearing, recondite applications of weaker versions of spells other paths do better etc. It does do several of these things without much muss or fuss though, meaning it is best used when deployed in its niche and not deployed without a plan or as a panacea.
Combat Spells
Summon Fire Elemental
- Fire Elementals are excellent at wiping out cheap chaff, skeletons, bugs, lightly armoured humans and the like. Even without the ability to damage much due to fire resistance or heavy armour, they have a lot of hp, good MR, and are ethereal so they can 'block' enemies for some time.
Incinerate
- Weirdly good at removing thugs without fire resistance despite difficulty of casting it and range issues. Lots of fire mages happen to have enough fire (with Phoenix Power) to cast it compared to other 3X-requiring spells.
Bonds of Fire
Prison of Fire
- Like False Fetters, locks down low-MR guys for a turn. The burning, morale checks etc is irrelevant - it's a lockdown, for a turn. That's worth on elite guys with low MR. Works extra good on elephants.
Fire Storm
- Slowly kills large amounts of chaff (like large skeleton armies or big casts of bugs). Requires Flame Ward/Fire Resistance or Marble Warriors to protect your men if they're not heavily armoured or fire resistant natively.
Phoenix Pyre
- With a means to reinvigorate (usually only Soul Vortex works well enough for this) can provide conditional immortality to a thug or a wall of communion slaves.
Bane Fire
- Crosspath D/F, this is one of the few 'no u' spells in the game. No save, high damage, armour negating. Hard to cast, usually restricted to a few nations in the quantity you need to bring to do real damage.
Sulphur Haze
- An early means to generate a cloud, will kill things relatively quickly if they can be held inside and don't have poison resistance (due to the poison being AN and applied 3 times/rnd)
Flaming Arrows
- A highly overused spell, adds a 8AP fire damage as a rider effect on ranged attacks (not spells). The 8 AP applies separately, meaning units with 16 prot or 5 FR + at least 6 prot will largely ignore it, as well as being deprecated by units with high move speed (messes with projectile targeting), air shield, or regular shields. The main use is removing tarpitting (skeletons, bugs) by bringing some cheap shortbows along. If someone is fielding crap infantry and not buffing them, or low prot high damage elites (a rare thing) flaming arrows can help shred them.
- The reason this spell is often overused is that building archers costs gold and Fire Elementals can do the same job often more cheaply and portably. If you have archers for siege or hp anchoring purposes however, Flaming Arrows can help give them a bit more utility.
Solar Eclipse
- Useful if your troops have darkvision, and theirs don't. Ghetto Darkness
Globals
Eternal Pyre
- Provides
gems to power elemental use, or more usually, lantern-spamming.
Items
Lightless Lanterns
- The best research booster in the game, despite requiring const 6 these can be gamechangers if you have enough fire income. Far outstrips other research boosters, and is often the sole thing saving the anemic research of several fire nations.
Water
Water is a weirdly weak-yet-strong path. A few things water can do are really, really strong (Wave Warriors + Mossbody, uw w eles, Freezing Mist, bottle assassins) but many more are situational or meh, with even Quickening coming way too late. It's kinda telling that most of what makes water an okay/good path are things I suspect are unintended interactions or bugs.
Combat Spells
Summon Water Elemental/Ice Elemental
- Water Elementals do immense damage with their crush attacks, they are probably the highest melee damage unit in the game without buffs. Despite the difficulty of doing so, they are often buffed, with spells like Iron Warriors or Protection, Strength of Giants etc.
- Ice Elementals trample like earth elementals, but are tougher.
Grip of Winter
- If your troops are cold resistant, and you can buy enough time (quite hard actually), Grip of winter can fatigue out the enemy or lower their stats via fatigue.
Living Water
- Unlike most 'Living' spells, Water's little elementals have AP attacks and can be quite threatening.
Frozen Heart
- Very high in research. But kills thugs and even can be employed en-masse to delete elite infantry.
Quickening
- A very powerful buff, force-multiplies melee attacking in several ways.
Quickness
- Point buffs elite units.
Mossbody
- A powerful spell, adds a high percentage chance to toss an additional damage removal effect when people hit them. Works very well with stacking various defensive abilities on a thug or elite units, notably Temper Flesh/Liquid Body/Wave Warriors.
Wave Warriors
- A powerful defensive buff on elite or buffed troops that halves damage taken after prot is calculated. Part of the complete defensive sandwich of layered buffs.
Cleansing Water
- Kills elite demons and undead pretty good. Can be used to wipe skeleton hordes, but it's a bit messy for that job.
Freezing Mist
- An early means to generate a 'cloud effect' with AN damage, if enemy units can be held inside and don't have cold resistance, they will die very quickly.
Globals
Vengeful Water
- Provides a fair few commander assassinations of enemies invading your dominion. Probably one of the few defensive globals worth casting.
Maelstrom
- Like all 'gemgens' this can be worthwhile. Mostly for creating Vitriol armies or spamming bottles or the like.
Items
Bottle of Living Water
- Produces a Water Elemental as retinue. A key assassin item and a key anti-assassination item.
Summons
Manifest Vitriol
- Green Lions are expensive but their breath weapon can be quite potent if you have a way to 'anchor' the enemy in place (any kind of movement or potential for movement will see the breath weapon scattering wildly because dom5's aiming system doesn't work with non-stationary targets).
Air
Air is a path with some surprisingly potent subtle stuff (Mist, Storm, Arrow Fend) combined with awkward-to-cast-but-powerful buffs (Fog Warriors, Mass Flight) and a gem-expensive but powerful option in Air Elementals. Air really wants you to be able to pick your fights to correctly use the tools it gives you - you do this by having other plans/options and using the air ones to support those options not as your sole thing, or by controlling the timing of battles in other ways (such as via raiding). Several air tactics get much stronger if you have only a single big air mage, or a huge amount of 
2+.
Combat Spells
Summon Air Elemental
- Flying size 6 tramplers, Air Elementals are empowered by Storms (unlike Thunder Strike casts) and don't do lightning damage (trample is untyped or bludgeoning or w/e), making them often the air method of choice that isn't lightning based.
- They are very brutal to use on turn 5 or the like after nearly all troops have advanced, as they use a fly attack AI that often targets low prot targets (like mages) as well as being totally capable of wiping armies very swiftly. Targets with magic weapons can kill them fast however, and size 6 units can stop them indefinitely (their actual non trample attack is garbo).
Storm
- This spell stops units without Storm Power/Storm Immunity from flying which is key in some fights (although often you need a storm staff to stop them flying before your cast finishes). It also halves precision, making spells miss quite a lot, and eats half of all arrows fired. Finally, it allows you to benefit from Summon Stormpower, which increases Air by one.
- This all lends itself to a variety of uses, but often people put it up and then use evocations which is terrible as they tend to all miss. A strong use is just denying flying enemies flight, or putting up and then spamming elementals after summoning stormpower.
Mist
- In combination with Storm or on its own, this spell pushes precision into the nether regions. If you're relying on melee attacks and your opponent is relying on ranged ones, mist will only help you. Any time someone is spamming evocations, this low cost alternative will combine with line formation to make their evocations mostly miss.
Thunder Strike
- Despite being wildly overused, this spell is still quite good. It is countered by lowered prec, line formation, and SR 5 (the secondary effect is a big reason why you're casting it). It has a sideline in deleting thugs or SCs without enough SR with the primary spell effect of a high damage lightning square hit.
Wind Guide
- Helps your mages hit what they are aiming at, which is valuable. Doesn't totally remove the penalty from storm but can offset it enough to be sorta tolerable. Almost required if you are casting Tstrike. Has a little brother that can do in a pinch, Aim.
Lightning Bolt
- Despite only hitting one guy, lightning bolt ignores armour, has good precision, and negligible fatigue. It is surprisingly viable to simply lightning bolt things to death, from thugs to elites to even regular infantry.
Cloud Trapeze
- One of the two common ritual speed movement spells, cloud trap is useful for gem burning, catching raiders with a thug, deploying a thug somewhere far away, wiping armies with a countergeared SC, and sometimes even getting that important mage where he needs to be for a fight next turn.
Fog Warriors
- Part of the balanced buff sandwich, Fog Warriors gives every unit on the field Mistform which is a powerful defensive buff.
Mass Flight
- Part of your continental buff-fast, Mass Flight avoids tarpitting via skeleton-swarms and the like, allowing your nigh-invincible swordsmen to fly around stabbing anything that moves
Phantasmal Army
Ghost Wolves
Phantasmal Warrior
- These spells are very expensive and kinda bad tarpit, but they at least exist, and sometimes you want to tarpit enemies without any good spells to do the tarpitting with.
False Fetters
- Okay-to-good tiedown in general, but really shines vs low MR opponents
Call of the Winds
- Okay patrol/siege chaff if you can spare the gems, good mapmove + flying leader helps with logistics issues
Summon Great Eagles
- Much more siege power than Call of the Winds on Great Eagles who follow orders and can fight okay in melee so they die less to any break siege attempt. With a high mapmove leader (like a Gift of Reasoned Great Eagle) they can cross the map to instasiege down throne forts for a throne rush.
Arrow Fend
- This guy helps you out against Iron Blizzard, but also against people who thought 300 crossbows was a good idea. Line formation also works vs these foes, but if you want to use box formation for buffing, you can put up arrow fend and just largely ignore them forever.
Globals
Gale Gate
- Gives you precious
air gems, but hard to research
Dark Skies
- A defensive global that does something, makes morale based tactics (like wailing wind) vastly more effective, as well as seduction
Items
Staff of Storms
- Puts up Storm, mostly useful to stop units flying at you turn 1 before you can cast Storm natively (like Ozelotls). Sometimes used by people to enable storm use when they only have1 or 2 mages and their main source of A is from a god, but generally that is too expensive in A gems to be worthwhile
Nature
Combat Spells
Swarm - Only not bold because of how common PR is as a bless, these bugs tarpit and even kill things in enough numbers. They provide the common method for dryads to kill those they fail to seduce, and for any number of stealthy, cheap or fast n mages to raid weak PD by themselves.
Creeping Doom - A powerful tarpit maneuver, only wide aoe or trample removes these bugs in any kind of timely fashion
Wooden Warriors - Good due to being in alt with lots of other good stuff and being aoe 5, not great vs fire damage but a good pre-marble-warriors prot buff before that
Poison Cloud - A strong source of AN damage that wipes out anything that stands in it without PR for long. Can even kill PR 5 things with enough exposure, or PR 10 with extreme amounts. Doesn't stack with itself but stacks with sulphur haze/freezing mist.
Sleep Cloud - Puts units to sleep. Poison damage doesn't wake them up, other kinds do. Combine with poison for a deadly lullaby.
Foul Vapors - The infamous vapes. Kills pretty much anything without PR if given time. Sometimes that time is 'part of one round'. Hilariously easy to cast, hilariously effective. Defines the meta of the game.
Poison Ward/Serpent's Blessing - Strong largely due to vapes being strong, part of the mandatory vapes counters suite, also part of the buff sandwich
Mass Regeneration/Relief - Part of your healthy buff sandwich breakfast, although less important than some other parts
Growing Fury - An extremely important counter to Wailing Winds and other (rarer) morale attacks, can also be used for complicated things involving SCs, or to trigger berserk on units
Pack of Wolves - A fairly efficient way to turn gems into patrol or siege strength, the wolves are undisciplined but stealthy which can be nice for keeping them out of harm's way
Awaken Vine Ogres - In combination with an Ivy Crown, a relatively cost effective way to get high hp guys who are useful to attract enemy evocations and some targeted spells
Howl - Causes a small amount of wolves to appear at battlefield edges, which can distract enemy troops or mage targeting. Most effective over long battles, or under spells like Rigor Mortis which causes people to become increasingly unable to deal with small numbers of fresh wolves
Tangle Vines - A small aoe tiedown, not as good as other tiedown but sometimes you need tiedown to deal with high def sacreds
The Ravenous Swarm - Kills undead thugs pretty good, with fairly little fuss or muss, which is the main use for it
Globals
Mother Oak - Notable mainly for being much earlier than other globals, and fairly easy to cast. Worth casting but often contested.
Gift of Health - Often brought up for removing afflictions from undead, which is largely used for removing afflictions from Tartarians. However a stronger and much earlier use is increasing hp in dominion, which can in combination with various buffs make armies much tougher and inconvenient to remove, which is the use that leaves it plaintext rather than italic.
Gift of Nature's Bounty - An extremely powerful if lategame global that generally should result in a rush if used, as it quadruples your gold income (ish). This global can be a way for a smaller nation to remain competitive with larger ones in terms of income.
Items
Vine Shield - A Vine Shield can make an okay thug into one that can fight almost any amount of crappy infantry. Although more experienced thuggers often use things like pike/burning pearl instead, the vine shield retains strong ease of use and has the interesting side benefit of trapping crappy attackers in squares surrounding the shield-wielding thug, meaning the thug suffers less attacks (and thus can be used for things like def-tanking W elementals)
Astral
Combat Spells
Luck/Body Ethereal - Pretty strong early buffs, or buffs for elites (small aoe), can often do far more than you expect especially luck early on
Battle Fortune/Will of the Fates - Strong buffs, generally part of the buff sandwich
Antimagic - Only good vs certain stuff, but so cheap and easy to cast that you see it fairly ubiquitously just-in-case on any army worth a damn with S access and the research, can save your ass vs some things that terrify newer players (big mindblaster stacks, master enslave)
Mind Hunt - Good to wipe out lowish MR thugs, if you have pen items, and a mage you don't need to spend a fortune boosting up. Against armies it will generally hit some totally irrelevant commander at best, and even against thugs it will often bounce off or hit a scout or something instead. One of the only remote/ritual speed spells that hits a stealthy guy, and the only one really suitable for striking solo thugs. Don't use vs astral mages or stealthy astral mage nations.
Soul Slay/Enslave Mind - Good single target spells vs elites with not-huge MR, to kill single SCs without 25+ MR, or if you set up a communion to 'default' to these spells and have enough blockers. Using it vs armies with chaff and methods to do actual damage often will lead your casters shooting 3-4 enemies and then getting swarmed down.
Communion Master/Communion Slave - A big part of astral's strength, communions are very powerful if also quite finicky. If you want to not kill your slaves and cast a bunch of spells it can involve online calculations or math or whatnot. If you just want to boost up a guy to cast a few big buffs then give him a bow to fire or something, that's a lot easier. But either way it's still strong. Enabler spell that makes your plans stronger. Does not help you much if you don't have a plan.
Nether Darts - Strong and easy to use evocation, made more annoying by being a crosspath and also fairly high in a school people usually research fairly late compared to the other paths
Teleport - The other commonly used ritual movement spell, useful when you want to move fast or hit something before it moves at regular speed
Astral Shield - Surprisingly good personal buff, part of the typical 'communion slave wall' combo of personal buffs + blink to make tiny hard to kill guys you teleport around the field to blob enemies on them
Globals
Dispel - Dispel dispels global spells. This can be a major use for your pearls, as taking down globals - especially gemgen globals - can often be a major deciding factor in who wins the game.
Summons
Golem Construction - Golems are useful for a bunch of weird edge-case stuff due to being mindless commanders who you can gear into relevance or survival in melee. They notably don't run and will turn timer enemy armies if the army can't kill them, on top of being able to teleport onto those armies with a Starshine Skullcap (and gem burn them with a Crystal Coin as well). At the very least they can provide Mind Hunt protection or astral buffs on a non astral nation if you for some reason have a god with the right paths and enough gems to make them.
Death
Combat Spells
Revive King - Gives you a Mound King that leads undeads, if you don't have that natively, or don't want to spend a mage doing it. Notably can put anything he leads in line formation, due to having 80 undead leadership, even humans.
Horde of Skeletons/Raise Dead - Raise Dead is better but requires corpses, which Horde of Skeletons doesn't. A very overused tactic, but not weak despite that. The major weakness is that it requires many mages, meaning if it goes wrong it can lead to catastrophic losses. If you have these researched, mages will 'default' to them generally, which is the basis of 'skelespam' aka making so many skeletons your enemy can't reach your mages and eventually drowns in the Bone Tide.
Rigor Mortis - Often combined with skelespam (but works better with pre-existing skeletons) this spell fatigues out living people a bunch and makes them more vulnerable to skeleton attacks. Works on your own army, but nothing much resists it (even relief still leaves a lot of enemies with a bunch of fatigue).
Shadow Blast - Very solid evocation, but needs a gem.
Dust to Dust/Wither Bones - Can be very effective to wipe out enemy undead (especially elite undead) but suffers from range issues and mages defaulting to skelespam after script
Soul Vortex - Useful spell for SCs (if it doesn't add too much fatigue) and they are fighting living things, also useful for mages/communion slaves, to regenerate fatigue by eating the life force of their bodyguards (works best on regenerating guys like trolls, but also works on regular guys until they die)
Invulnerability - Ironskin-alike spell, doesn't work on magic weapons but can be okay outside of that circumstance if you need arrow immunity or w/e
Reanimation/Pale Riders/Carrion Reanimation - Sometimes you have piles of death gems and need some cheap chaff/fast horse chaff and you use these spells, it's not pretty, it's arguably quite inefficient, but it is a thing you do
Bane Fire - A very strong spell that basically says 'no, u' to quite a lot of things. Annoying to cast and in practice restricted to a short list of specific nations.
Twiceborn - A spell that allows you to risk rare randoms or cap only guys casting spells on the field with the knowledge that if they die they'll come back. Not foolproof, and not perfect. People advocate this as a way to remove upkeep from mages which is frankly an immense waste of death gems but if someone's sitting at 788 upkeep from 800 income in their 6 province empire on turn 48 they do all kinds of crazy things I guess.
Darkness - Massive force multiplier for anything that sees in the dark, including skeletons and soulless.
Wailing Winds - Hugely powerful morale spell. Anything with morale will run away unless huge morale (18+) or berserked. Worth casting pretty much always if you can.
Wind of Death - Effectively a battlefield-wide save-or-die. Decay is brutal. Can be used on your own armies if you have higher MR than your enemy/are buffing antimagic and they aren't. Also can be used by a mage with a bit of chaff (the chaff dies) to whittle at the enemy while risking little of your own, with or without twiceborn/ring of returning etc.
Bone Grinding - Very strong but also very hard to cast, rarely able to cast outside pretender god or communion, but still worth doing sometimes.
Stygian Rains - If you have the paths and the research and magic weapons and your enemy doesn't, it's a good spell to cast. This is a rare set of things to have, but Atlantis has it quite a bit.
Life after Death - Late in the game and annoying to cast, worth putting up, sorta worth suiciding mages/priests in for various reasons although people often focus on this part too much or go up ench for that part alone
Various mage summoning spells (Lichcraft/Call Wraith Lord/Summon Mound Fiend/Create Revenant) - Worth if you need more D mages of that level of path, and the immortal guys are nice to empower in A for Wailing Winds/Wind of Death (safer than Ring of Returning) but people make way too many of these guys
Items
Skull Staff - A cheap booster that enables quite a lot of shenanigans, the Skull Staff will see use with most death nations, being not quite as common a sight as your quintessential Erf Boots but still very common. Used to allow summoning of higher D mages, but also to cast wind of death/wailing winds/darkness, the ol' skull on a stick will be a useful tool in your arsenal pretty much always.
Blood
Combat Spells
Leech - Kills the hell out of anything it's in range for and reinvigorates your mage, excellent artillery that will utterly blat thugs coming to disrupt your blood hunting
Life for a Life - Leech but no reinvigoration or AOE but also no range issues and hits super hard
Reinvigoration - Wipes the fatigue of your communion or sabbath, can knock out a mage with a big fatigue spell then spam reinvigorate, to make a guy past turn 5 be reinvigorating for longer lasting communions
Summon Imps - Surprisingly non-terrible, Imps are tiny slashers with wings who will do much better vs low prot targets than high prot ones.
Blood Rain - Lowers enemy morale, but weaker than Wailing Winds. Still worth casting in general but best used comboed with other fear tactics.
Rush of Strength - Battlefield-wide Strength of Giants. If you already have strength of giants this isn't exactly gamebreaking but it's still nice to have. Earlier version for demons only is Blood Lust.
Sabbath Master/Slave - Same deal as communions, but less good due to the fatigue the spells give to guys entering it and requiring a slave per cast
Bind Fiend - A bit annoying to mass, but Fiends of Darkness are extremely strong when point buffed, especially if you are able to cast Darkness. Italic because you need to be able to mass them, and to be able to buff them - once you can do both those things they are terrifying.
Bind Storm Demon - Just as annoying to mass, but perform better with few buffs than Fiends of Darkness, especially vs enemies that are not shock-resistant and have low move/clumped
Bind Devil - Just as annoying to mass, but perform better vs shock resistant foes, when you have few buffs, and the enemy is vulnerable to attack rear. Essentially Fiends (with buffs) > Storm Demons (without buffs + non shock resist)
Purify Blood - Basically Serpent's Blessing, so an anti-FV spell, but in blood? Good if you've only got low nature and the blood crosspath. Worth mentioning mostly cause FV exists, but at that stage it may be easier to toss flying blenders at the problem rather than buff up with anti poison.
Bloodletting - If spammed, some niche use in wiping out armies that don't buff MR
Send Lesser Horror - Can wipe out PD, meaning a scout moving in from an adjacent province takes the 0 PD province after the horror leaves, bit iffy sometimes though depending on pd levels
Infernal Disease - Powerful spell if enemy has mages that die to disease demons, remote assassination is pretty strong and it costing slaves is a big plus. If the enemy has bodyguards on his mages the strength drops off a bit though. Biggest weakness is needing usually 2-3 boosters to make a mage that can cast it. The 5-slave cost seems small but can start to eat into your blood income, if it's taking 3-4 casts to kill bodyguarded/gemmed/summoning enemy mages.
Globals
All blood globals are sometimes worth casting with a big overcast, as your (relatively) cheap slaves can dispel another global in a full global list, or deny a slot. Slaves only count as half a gem for overcasting, but you can have so many that it doesn't matter that much. Note the sometimes. Don't spend hundreds (or thousands) of slaves on a global 'just cause' - that's hundreds of Fiends of Darkness. But it is, sometimes, a good idea.
Blood Vortex - Cast on your cap/another cap, the highest pop province you can find. Doesn't eat pop from that province - draws it from far away via events. Gives slaves based on the pop of the province you cast it in though, so like 50/turn or something which often pays itself back quite fast.
Astral Corruption - Basically declares war on the world, but can put a crimp in nations doing a lot of forging or (somehow) summoning. Doesn't really stop people as usually the big thing is casting buff spells in combat rather than summoning or forging but it can be a nice ♥♥♥♥-you to some nations (like agartha) that actually have good summons to use.
Items
The Black Heart - Turns a stealthy guy into an assassin. This is about as broken as it sounds, yes.
Summons
Curse of Blood - Makes a 
3
3 flying stealthy mage for 77
. Very good for blood spells, or for stuff like casting Darkness. People fixate on the immortality and try to use them as skelespammers or raiders, or to blood hunt when they don't have native blood, which largely misses the point of their mobility and high paths. Alone they are easy to get soul slayed or just be irrelevant - casting big buffs or SC removal spells, they are far more relevant and worth their cost/the research to get to that level of blood. 15 Vampire Lords casting Horde of Skeletons or 2 Vampire Lords casting Darkness and Blood Rain/Rush of Strength + 200 Fiend of Darkness ripping and tearing, one of those two things is much stronger and scarier.
Father Illearth - Makes Pedoseion - Father Illearth, a very tough SC chassis who also casts pretty much any earth stuff you want casted. Worth buying in general if you have the paths and reasons to go that high in blood. Can be worthwhile going to that level of blood for if you have a requirement for a tough SC chassis and don't have one otherwise. One of very few guys in the game who can shrug off meteors or piles of damage that would kill lesser SCs, making countergearing enemy armies significantly easier.
Gemgens, Boosters, and Summonable Mages
I have not listed every gemgen global, booster item, rp booster, or summonable mage in the game. Because when it comes down to it, they are all good situationally. If you have the gems and the research, there is little reason not to buy them when you need them or can afford them.
- Summonable mages that give you access to new paths or higher levels of paths or paths you only have few mages of are good, if you can afford them without denting your war-treasury of gems you'll need to cast big buffs/debuffs in wars.
- Booster items that let you cast big buffs and the like are good, if you can afford them without denting your war-treasury of gems you'll need to cast big buffs/debuffs in wars.
- Research boosters that give you a push in research are good, if you can afford them without denting your war-treasury of gems you'll need to cast big buffs/debuffs in wars.
- Gemgen globals are amazing, if you can afford them without denting your war-treasury of gems you'll need to cast big buffs/debuffs in wars (although often, with these, they pay back so fast you can still fight immediately as long as they aren't dispelled).
Notice a running theme here? The biggest problem with these items isn't that they aren't good, but that people empty their bank to do them, then run out of gems, then get in a war in which they cannot afford to field the number of armies they need to with the buffs those armies need, due to lack of gems. Or they don't declare war - to save up gems - when they absolutely need to fight someone to get enough land to remain in the game vs people who are gaining more land than them.
There's another problem with people who never spend any of their gems (hoarders?) and die with like 2000 unspent gems in treasury, but I'm going to assume that people reading this guide are actively going to attempt to spend their gems in useful ways.
There's a bit of a secondary concern - Winged Helmets are more efficient than Bag of Winds, Skullface is hilariously expensive if you can get by with a Skull Staff and a communion master Crystal Matrix, Owl Quills and Skull Mentors are much less efficient than Lightless Lanterns, so there's all that guff but I'm hoping it's all fairly apparent when you look at the things and see what they do and for how much so I'm going to leave all that as read and simply say -
If you can afford to create this stuff without emptying your war-treasury, then doing so is often a good idea. Which things, and how much of a good idea, really depends on your situation quite a bit so you will have to decide, for yourself.