Some units have special abilities no other units have. Here is a list of abilities in Ultimatum.

Units with the Regeneration ability recover 4 to 8 health per turn. Units like Trolls have this ability.

Units with the Nightcloak ability become invisible during the night time. They become visible when they adjacent to an enemy, an enemy moves close to the unit, or if you attack an enemy unit.

Skirmishing units are able to ignore an enemy unit's Zone of Control. However, they cannot move through the unit's territory if they are level 3 or higher.

Units with the Leadership ability help lower-leveled units do better in battle while adjacent to them. They do one point more of damage for every level in difference.