If a player uses Deathknell to flip a hidden Tide Caller and swap in Mundo during a showdown initiated by the opponent's Kaisa, does it start a new showdown between Kaisa and Mundo?

Ruling: No, this does not start a new showdown. The attacker conquers the battlefield normally and the swapped-in unit remains there without combat occurring.

Sequence:

• Opponent moves in with Kaisa, starting a showdown
• In response to Sentry dying, Deathknell triggers to flip hidden Tide Caller and swap in Mundo
• Special cleanup during combat does not clear contested status until after Deathknell resolves
• The player still controls the battlefield until contested is cleared
• After cleanup completes, the attacker conquers normally

Nuances:

• The attacker does not recall to base; both units remain on the battlefield
• Contested is not cleared until after the special cleanup during combat
• A player still controls the battlefield until contested is cleared, allowing the Deathknell trigger to resolve
• This creates an unusual but legal board state where both units coexist without combat