Pointy-eared Elvish princeling.G 10

You can do this on -Amon Hen- when you fight the Urak-hai at the end of the LVL just don't hit the boss(up on the top ledge,you have to crawl through a hole to hit him with a small character),untill you've killed 42 Urak-hai that run from the sides.They will continue to re-spawn as long as the boss is there.Achievement will pop in gameplay so you'll know when to finish the boss/LVL.