Rampage

Rampage is a  passive skill in Diablo III, unlocked at level 68.

In-game
This buff is not multiplicative to other similar modifiers, but since it increases Strength rather than damage, it will stack multiplicatively with most other damage enhancements. The effect does trigger off Illusionist affix dummies, as dispersing those does count as killing blows.

This passive is certainly powerful in particular for a Barbarian who wishes to go far in Greater Rifts; not only is it a very beneficial aid to both damage and toughness, but it is also easily refreshed, especially due to the nature of the 15 minute timer.