GreError
It is extremely easy to get GreErrors causing the game to end in a draw when in reality you should win. With ratadrabik on the board with Mondrak if you play Jaxis for it's biltz cost, use his ability to target ratadrabik and usually this is enough to cause the game to lock up until it ends with GreError Winner: Draw. However there are other ways to do it such as vesuvan diplomacy with mondrak or ratadrabik, can also be caused with things like ratadrabik and drivnod, or anything that causes a bunch of tokens with a creature that triggers on creature entering the battlefield such as lunarch veteran or Elas-il Kor.

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tink#45835 commented
This also happened to me when casting Doppelgang with X=10, targeting various mana producing creatures and artifacts, and:
- Nyxbloom Ancient
- Kinan, Bonder Prodigy
- Primeval TitanSome of them were token copies, not the original cards.
I also could tap around 50 mana before casting it.
I can understand why there need to be limits, but tell me and make me choose a smaller X, don’t draw the game.