See you in Hell - S8.E6

Mom strokes out in a bar and dies, Percy slowly succumbs to necrotizing fasciitis, Marty fails at suicide but dies anyway and all the while Mr. Franklin (we don't really know it since in season 1 episode 8 we discover that there are two 'twin brothers' with the same nickname Mr. Franklin), Kevin’s first psychiatrist from season one is on a manhunt to destroy the boy. Eventually those left living cross paths, and the true nature of Kevin’s brain problems are revealed.

In the end Allen the Goose enters the Morgue where Kevin took his mother's corpse (after Kevin dies by a car accident saying 'Good bye Allen') and is revealed that all the series and characters (even Kevin himself) are imagined by Allen due to certain Psychiatric problems.