Stray Blade

This will be unlocked around the time after killing the first big boss in The Cradle zone. Some areas have respawning enemies, but not all, and the run back will have you kill them again or flee past them. It's up to you how you handle enemies.

Anyways, once you reach level 24 you will have enough skill points for this to unlock. Just go in your skill tree and find a skill you like and spend the points.