In a showdown, after starting a chain with a spell and it resolves, does the attacker retain focus to immediately cast another spell, or does focus automatically pass to the opponent?

Ruling: Focus automatically passes to the opponent after a chain resolves completely. You cannot cast multiple spells in sequence while maintaining focus.

Sequence:

• Player with focus starts a chain by casting a spell
• Chain resolves completely
• Focus automatically passes to opponent
• Opponent can start a new chain or pass focus back
• If opponent passes without starting a chain, focus returns to original player
• Original player can then start a new chain or pass
• Showdown ends only after both players pass focus sequentially without starting a chain

Nuances:

• Priority is retained when putting something on the chain, but focus is not
• If you start a showdown and immediately pass on an empty chain, then opponent passes, the showdown ends immediately
• You can cast multiple spells in the same showdown, but only by regaining focus after opponent passes, not by retaining it after your chain resolves