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You may look at face-down creatures you don't control any time.
Keeper of the Lens allows you to look at face-down creatures you don’t control whenever you want to, even if you don’t have priority. This action doesn’t use the stack.
Keeper of the Lens doesn’t let you look at other players’ face-down spells while they’re on the stack.
Keeper of the Lens doesn’t stop your opponents from looking at face-down creatures they control.
