SHReK the THiRD

You will get this throughout the normal course of the game. When fighting enemies you will see a "Y" appear over enemies, when this happens press "Y" and Shrek will perform a finishing move. Unfortunately there is no way to skip the little animations and they are repetitive and boring, but alas do 100 of these finishing moves for the achievement.

The best level to do this on is "The Royal Tutorial" Its the first level in the game. You will have an unlimited supply of enemies so long as you avoid blocking. Then simply hit an enemy until you see the yellow "Y" above their heads and then press it to perform a finisher. Simply repeat for a total of 100 times and the achievement is yours.