He prided himself to be the toughest, most ruthless man in the world, shrugging off torture, ignoring such petty things as morals, and looking forward to breaking Death's neck. When he was brought to justice, with a record-breaking list of charges, and proud of it, finding a punishment that would faze him was problematic. Death was too easy.
The solution was easy, too, once someone thought of it. They chucked him through a one-way worldgate.
Once he realised the alway-cheerful cute animals made of marshmallow did not mind getting ripped to shreds, he knew he had lost.