Tournament rule 703.4.b.3

If the error is caught by a player other than the erroring player after opening hands have been drawn, the penalty is upgraded to [Game Loss].

• 703.4.b.3.a At casual or competitive OPL, if the error is a player forgetting to move their Chosen Champion from their Main Deck…
• 703.4.b.3.b Players may request a judge check an opponent’s deck for legality. (Example: A player believes an opponent has a…

Official Tournament Rules