RulingRules Reference 1.8

When Marked for Death is revealed, if a copy of Mockingbird is already under a player’s control who is not Clint…

Question

When Marked for Death is revealed, if a copy of Mockingbird is already under a player’s control who is not Clint Barton, what happens?

Answer

The Clint Barton player can tuck their copy of Mockingbird under this scheme even if there is another copy of Mockingbird in play because tucked cards are not considered to be in play.

— Rules Reference 1.8