Is there an official source for how judges should handle illegal plays, wrong setups, or cheats, and what happens if someone forgets to place their chosen champion or draws too many cards by accident?

Ruling: There is an official tournament rules document that covers how judges should handle illegal plays, wrong setups, and cheats.

Nuances:

• If a player shuffles their chosen champion into their deck (deck presentation error), the penalty depends on who catches it: if the player catches it themselves after drawing opening hand and calls a judge, it's a warning; if someone else calls it after opening hand, it's a game loss
• Accumulating 3 warnings of the same type in one day of an event results in a game loss