some like, when Unit-A is attacked by Unit-B.
Unit-A cause damage on B ( some effect is nice, but not too much for this is a combat map )
Other is
Unit-A attacked B, A cause damage on B.
Should have (15+level-passive-skill)%.
Other is, when User cast a spell, User got a buff, and next attack will cause bonus damage
( not really my idea, got it from other map like dota, and things)