New to Dominions 6, Mounted units are treated as different entities from their Mounts. The mount may be hit instead of the rider, for example, and one can outlive the other.

When a foe performs a melee attack or a missile attack on a mounted unit, they prefer to aim for the rider. This presumably because most mounts (or at least most horses) will rout if they suddenly find themselves riderless. However, the Size of the mount (especially in comparison to the rider) and the Reach of the attack will mess with this.

• First of all, before everything else, a roll is taken to see if the rider can hide against their mount. If the mount is 3 size points larger than the rider, there's a 25% chance that the mount will be targeted; a 4-point difference makes the chance 50%, and a difference of at least 5 points makes the chance 75%. Size gaps of 2 or lower don't allow for successful hiding, resulting in this roll being skipped.
• If the above roll "fails" (as in, if the 25-75 percent chance doesn't happen) or is skipped, what happens depends on whether the attack is a melee one or a missile one.
  • For melee combat, there is another chance to end up targeting the mount instead of the rider. The minimum chance is 10%; this is attained by having a Reach that's 2 points greater than the Size of the mount. A difference of 1 makes it 20%, a lack of a difference makes it 30%, and having a Reach 1 point less than the Size of the mount makes it 40%. If the Reach is 2 points less than the Size of the mount, or lower, the mount will always be targeted.
  • For missile combat, the rider and the mount have an equal chance of being targeted, at least at this stage.

For the record, if a mount has multiple riders and a rider is targeted, which rider gets targeted is selected at random. The biggest rider's Size is used for determining the chances for that first roll, though absolutely no units currently in the game have riders of heterogenous sizes.

Just for an example of the missile situation, say an Archer is trying to hit the Elephant Rider on a War Elephant. Say the projectile ends up in the War Elephant's square, and say that there isn't an un-mounted unit sharing the square to get targeted instead. The War Elephant's Size is 9, while the three guys (the Rider and two Archers) on the Elephant are each Size 3. Only one rider's Size is counted, and the size gap is over 4, so the War Elephant has a 7-in-8 (3/4 + 1/4 x 1/2) chance of being targeted. The remaining 1-in-8 chance of being hit is equally divided between the three, so the Elephant Rider proper has roughly a 1-in-24 chance of being shot.

There are a few special hits that will only hurt a mount, and not their rider. Trample, for instance, will only hurt a mount. The same is true for the Earthquake spell, though not for the portion that only happens in Caves.

What hits can hit both a mount and their rider? All area-of-effect ("AOE") hits, other than Trample or Earthquake. All Shock Attacks, too.

A rider uses their mount's Map Movement and Combat Speed. The rider also suffers only half as much Encumbrance from gear as unmounted units. On the other hand, the mount suffers additional Encumbrance from carrying riders; this appears to depend entirely on the Size of the rider relative to the Size of the mount, and not on the weight of the rider's equipment. The formula appears to be [3 + (Rider's Size) - (Mount's Size)], down to a minimum of zero. How much space the combined unit takes up, in Size points, is listed in parenthesis.

For all combat purposes, primarily Encumbrance from Flying and the Curse of Stones, only the mount is considered to be moving around in battle. This was a very recent change to the game, circa 8/26/24.

The rider and the mount both get to attack in their combat round, as though they are different units, though the rider suffers a -3 Attack Skill penalty with two-handed weapons. The rider gets +3 Defence Skill, should they be targeted instead of the mount for some reason; this is a bonus from very early in the Dominions series.

There's a Skilled Rider trait some riders possess, which provides Defence Skill and Morale bonuses to their mounts. The Defence Skill bonus is reduced by whatever Encumbrance penalty the mount has from their armor, however.

For mounted commanders, only some items benefit both the rider and their mount, given how they are different beings. Most of them take up miscellaneous slots, which mounts typically lack. Most mounts have a Barding item slot, allowing them better Protection and some other effects.

Mounted units don't ever dismount, at least by choice. Usually the rider is thrown off the horse by an individual Morale check the mount fails, which is typically caused by a Fear effect. Alternatively, the mount might just die.

Forced dismounting (or the loss of a mount) causes falling damage; in this case, the damage is 1d[(Mount's Size) - (Rider's Size)], though open-ended. This damage ignores Protection on the rider. Riders of Chariots do not have this issue. The rider fights on afterwards; unless whatever caused the mount to rout also caused the rider to rout, of course.

Mounts do not take squad Morale checks. Thus, in most routing situations, only the rider's Morale matters. If (only) the rider routs, they stay on their mount while doing so.

In the case of the rider dying, mounts will lose their Skilled Rider bonuses (if they had any) and then undergo an individual Morale check to see if they rout. The difficulty for the individual Morale check here seems to be higher than it normally is, possibly a 10 instead of a 6.

Units can, in fact, persist in their dismounted (or riderless) states. If they make it back to where they were recruited, they can regain their other half at half cost, retaining their Experience and everything else that makes them unique. The catch is that they will undertake this journey back to where they were recruited on their own, being uncontrollable during the odyssey.

Most former mounts will not persist after the battle, however; only Smart Mounts do that. The trait comes with a percent value; this is the chance that they'll persist in their quest beyond each turn. On turns/months where they persist, there are still trials in the way that may prove too much to bear; this is abstracted as an individual Morale check with a difficulty of 6, which causes the mount to disappear if they fail.

All riders operate as though they have Smart Mount (100). In fact, if a dismounted rider and a compatible riderless mount are in the same province outside of combat, they will match up and combine into a mounted unit. It isn't clear how riders who normally share mounts handle this situation.

The manual says that, in the turn order, mountless riders and riderless mounts decide what to do in between Assassinations and troop movement.