Case of the Burning Masks

(1) (R) (R) 

When this Case enters the battlefield, it deals 3 damage to target creature an opponent controls.
To solve — Three or more sources you controlled dealt damage this turn. (If unsolved, solve at the beginning of your end step.)
Solved — Sacrifice this case: Exile the top 3 cards of your library. Choose one of them. You may play that card this turn.

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