If P1 controls both battlefields and P2 charms a unit from BF1 to BF2, but P1 retreats their unit from BF2 in response (before charm resolves), does P1's arriving unit start a showdown to score when it arrives at BF2?

Ruling: Yes, a showdown will start and you'll gain a point if you re-establish control.

Sequence:

• P1 retreats their unit from BF2 in response to charm
• Cleanup establishes the battlefield as uncontrolled immediately after the retreat effect resolves
• When P1's unit arrives at BF2, a showdown starts
• P1 can score if they re-establish control

Nuances:

• P1 lost control of the battlefield when they retreated the unit, even though they controlled it at the start of the turn
• The battlefield becomes uncontrolled in the window between the retreat resolving and the arriving unit