Case of the Filched Falcon

Enchantment — Case
When this Case enters, investigate. (Create a Clue token. It's an artifact with ", Sacrifice this token: Draw a card.")
To solve — You control three or more artifacts. (If unsolved, solve at the beginning of your end step.)
Solved — , Sacrifice this Case: Put four +1/+1 counters on target noncreature artifact. It becomes a 0/0 Bird creature with flying in addition to its other types.