What happens when Kayn starts a showdown while invulnerable but there is more might on the board than Kayn's might?

Ruling: Kayn bounces to base, killing whatever he can during the showdown.

Nuances:

• Kayn's invulnerability lasts until the end of the turn, not just until the end of the combat
• When attacking units survive combat (whether from another battlefield or not), they are always recalled to base, not back to their origin battlefield