When The Good Time Sleuth enters, exile the top card of your library and each nontoken creature you control in a face-down pile, shuffle that pile, then manifest those cards. Then create a Blood token for each face-down creature you control. Those creature gain "Sacrifice a Blood: Turn this creature face up." Secretly choose one of them. As that creature is turned face up, reveal the choice and it becomes a 5/5 black Demon.