Case of the Stashed Skeleton

When this Case enters the battlefield, create a 2/1 black Skeleton creature token and suspect it. (It has menace and can't block.)
To solve — You control no suspected Skeletons. (If unsolved, solve at the beginning of your end step.)
Solved — , Sacrifice this Case: Search your library for a card, put it into your hand, then shuffle. Activate only as a sorcery.