If I play Challenge during a showdown to kill my opponent's attacking unit (using a unit from my base), does the showdown end immediately or continue, and does my defending unit survive?

Ruling: Challenge will kill the opposing unit, but the showdown does not end immediately. Players continue to have the opportunity to play spells back and forth until both pass, then the showdown ends.

Sequence:

• Challenge is played during the showdown
• The targeted opposing unit is killed
• Showdown continues with spell opportunities for both players
• Both players pass
• Showdown ends and might is allocated
• The defending unit survives because the opponent has no units left to allocate might

Nuances:

• Even though the attacking unit is killed by Challenge, this does not immediately end the showdown phase
• The defending unit survives because during might allocation, the opponent has no units remaining to deal damage