One who goes unpunished never learns.

You’re the Head and only judge of a Standard GPT. Andy is playing against Nick. Andy controls a Liliana Vess and he activates Liliana’s -2 ability, searches and finds a card. He then shuffles his library and puts that card on top of it. Andy then attacks with a Grim Haruspex, and Nick blocks with a Bronze Sable. They go to combat damage, both creatures die, then Andy says “draw for Haruspex” and draws a card immediately. Nick reads Grim Haruspex, points out that the card shouldn’t have been drawn, and calls a judge.

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Answer
As many of you determined, the infraction here is Drawing Extra Cards. Andy needs to reveal his hand, Nick will get to choose a card and that card will be shuffled into Andy’s library. Even though Andy knew the identity of the card, it was not known to all players, so policy doesn’t support a fix that would result in the chosen card ending up on top of Andy’s library.

Paul pointed out the possibility of interpreting this as “adding the draw trigger to the stack was actually the error rather than drawing the card.” As Mani points out, the philosophy of DEC is to cover draws which the opponent has no opportunity to prevent. Because Andy pointed out the non-existent trigger and resolved it all at once, there was no such opportunity.