At competitive OPL, can a player take back an attack declaration after forgetting about Master Yi Legend's +2 Might ability when their unit enters combat?

Ruling: No, the attack cannot be taken back at competitive OPL. This is a legal misplay, not a gameplay error, and rewinds at competitive events are reserved for illegal moves or broken game states.

Sequence:

• Player declares attack and unit moves to battlefield with Master Yi Legend
• Combat begins and Yi's +2 Might ability applies
• At this point, new derived information becomes available and it's too late for a takeback

Nuances:

• At casual events like Nexus Night, judges may allow takebacks for such misplays
• Players are not obligated to help opponents calculate derived information like combat math
• Players must answer truthfully about board state and public knowledge when asked (e.g., current Might values)
• However, players don't need to remind opponents about future state changes (like Yi's +2 when combat starts)
• The information about Yi's ability is public knowledge, but calculating its application is derived information