You will come across the Leviathan at the end of chapter 6.
He is a very huge boss. At the very beginning of the battle white worm like things will shoot out from underneath it, quickly shoot the yellow parts of them to kill them. After all 3 are dead, it will shoot exploding rocks at you from the middle of its mouth, while its' shooting catch them with Kinesis and shoot them back for the 'Playing Catch' achievement. After you get it just shoot them before they leave his mouth and it will hurt him more. Keep shooting them and it's dead. I finished it in under 2 minutes on easy.