You are the Head Judge for a Modern PPTQ. On her first turn, Andrea plays a Swamp, then casts Inquisition of Kozilek. Naomi reveals her hand: three Plains, two Path to Exile, and two Thraben Inspector. Andrea writes down every card in Naomi’s hand, and when finished, says “pass the turn.” Naomi picks up her hand, draws a card for turn, plays a Plains, and casts Thraben Inspector. At this point, Andrea realizes she forgot to pick a card for Naomi to discard, and she calls for a judge.
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Andrea receives a Warning for Game Rules Violation, and Naomi a Warning for Failure to Maintain Game State. Plains and Thraben Inspector were both cards known to Andrea from the Inquisition of Kozilek’s effect, and nothing else has happened, so backing up is appropriate. To do so, return the Thraben Inspector and Plains back to Naomi’s hand. Then pull aside the card Naomi drew for turn, the only card not listed on Andrea’s list of Naomi’s hand, and put that card on top of Naomi’s library. Finally, we will put Inquisition of Kozilek back on the stack, and reveal Naomi’s hand again, to have Andrea select a card for Naomi to discard.