Horror marks can be applied to both units and commanders by various effects, and will cause horrors to have a random chance to attack the unit in an assassination setting at the beginning of every turn. In addition, horror marked targets are preferred targets for any horrors spawned in normal battles. A unit that is horror marked will have the icon displayed alongside its other abilities.

Horror marks stack: that is to say that a unit which is marked multiple times has a more severe mark, though besides the frequency and strength of horror attacks, there is no way to tell how badly horror marked any given unit is. There is no way to remove a horror mark entirely, though for units that may return once slain, horror marks are reduced every turn spent dead.

• Guaranteed when casting Hell Power, when affected by Horror Mark (1) or the primary effect Astral Geyser (2)
• Chance per turn when holding a tainted magic item (1)
• Chance per turn when in a province with certain magic sites
• 1 or 2 when empowering in Blood: 7.5% per level of blood prior to empowerment, or 25% if the commander had no blood levels¹⁾.
• Chance when casting certain spells such as Send Horror
• Certain global events, such as that caused by the Vale of Infinite Horror being discovered (a certain percentage of units must make a MR check vs 16, -1 per two astral levels, or gain one mark)

When hosting a turn, there are three different destinctions used by the game when deciding to send a horror assassination to a marked commander. First, the game considers "normal" horror assassinations. After this, there are then additional separate chances to send Umor - Eater of Gods to marked pretenders and Rarku - Hunter of Heroes to creatures in the hall of fame.

The attack rate of horrors is dependent on several factors, and is calculated by the game as follows²⁾:

• Get the count of Horror Marks on the affected commander.
• If this number is greater than 100, consider it as if it were 100.
• The "attractiveness" value is first calculated as (mark count * 5) + 1.
• If the unit is holding a cursed item, add an additional mark count * 5.
• The final attractiveness is calculated as:

  (Attractiveness - Drain + Misfortune) * Global [[Horror]] Level

• Generate a random number between 0 and 999. If the random number is less than the calculated attractiveness value, the commander is attacked by a lesser horror.

The global Horror level varies as follows:

The resulting lesser horror attack is subject to the usual upgrading process and multiplicity described in the Horror article.

Due to the multiplication, the effect of scales on the attack rate is largely negligible unless the global horror level increases dramatically.

In a normal game state with a global horror level of 1, horror marks are approximately 0.5% per mark per turn to produce a horror attack, which is then doubled if the commander has a cursed item. This is consistent with experimental data ³⁾

Testing for the Eater of Gods on pretenders suggests that the attack rate may be roughly constant irrespective of the number of marks. If both Astral Corruption and the Cataclysm are inactive, this attack rate appears to be (1% + 0.2% per mark) to a maximum of 5%⁴⁾. Otherwise, the attack chance is (1% + 2% per mark), to a maximum of the global horror level. Pretenders are subject to this in addition to the normal mark attacks.

The chance for the Hunter of Heroes to attack eligible commanders is initially calculated the same way as the Eater of Gods for pretenders, but is doubled at the end.

Mark reduction for dead commanders is by 10% of their mark count per turn, rounding down. The mark count will be reduced by a minimum of 1 mark per turn with the only exception that it cannot reduce a unit's marks to 0.