Defiant

This is a Generation V ability. It increases attack if stats are lowered.

Pokemon who really have this ability
Komatana and Kirikizan.

Pokemon who have this ability in the Dream World
In the Dream World, Mankey, Primeape, Farfetch'd, Piplup, Prinplup, Empoleon, Purugly, Wargle, Tornelos, and Voltolos.