A debuff is a temporary, or one off, reduction of an enemies hero(s) ability/attribute(s) that typically comes from hero's skill proc or a talent / crest.
Debuffs / debuffers typically target:
- Reducing attack(ATK) (amount of damage and damage from skill / proc)
- Reducing the move speed (MOV SPD)
- Reducing the attack Speed / Rate (ATK SPD)
- Reducing the energy of a hero
- Increasing how much damage a hero will take.
Heroes with debuff ability can typically apply a debuff's to enemies and not allies or self.