Awesome! Thanks everybody.

yea when he turns into a "God-Liaith" thats his last level.... i got the achievement on PS3, took me awhile but you'll get it :)

Thanks!

Perfect! "The Once and Future Slab" is a good chapter to get the achievement. Use a lower level gun and try to shoot any of the other baddies to soften them up for him, since he'll attack anything around him. He'll keep leveling up as he starts killing the other enemies and long as you make sure he doesn't die. Try to stay away from him until he's ready to go down for the achievement. If he does die before he hits level 4 or an enemy kills him right after, see if you can restart from a previous save.