Centaur Warrunner has a passive ability, "Return":
Centaur Warrunner immediately counters every attack, damaging the attacker based on a percentage of Centaur's strength.
Base Damage: 16/18/20/22
Bonus Damage as Percent of Centaur Warrunner's Strength: 26%/34%/42%/50%
Source: http://dota2.gamepedia.com/Centaur_Warrunner
If an enemy hero uses a DoT ability, does Return activate on each instance of damage and do "returned" damage to the caster?
Best Answer
Centaur Warrunner's Return does only proc on attempted attacks and therefor does not return damage from skills including damage over time.
Furthermore damage from units (for example Venomancer's wards) wont trigger Return on the hero.