Special ability

Special ability is a term typically referring to a creature's ability to actively or passively do something other than basic melee attack in combat. Active special ability means, that the creature has to act in a specific way for the special ability to emerge. For example, wyverns poisonous ability requires them to attack or retaliate. Passive special ability means, that the creature does not have to anything to use it. For example undead is an special ability of all necropolis creatures, which makes them immune to certain spells among other things. A passive ability could be considered a characteristic of a creature.