When a showdown is initiated and a reaction (Stupefy) is played and resolves, can an action (Cleave) be played next, or can only reactions be chained after an action?

Ruling: When a card on the chain resolves, that chain closes. After a chain closes, the active player regains focus and can start a new chain with either an action or a reaction.

Sequence:

• Player initiates showdown and may play an action or reaction
• Opponent responds with Stupefy (reaction)
• Stupefy resolves, closing the chain
• Focus passes back to the active player
• Active player can now start a new chain with Cleave (action) or any other card
• Combat damage occurs only when both players pass without starting a chain

Nuances:

• Resolving the last item on a chain closes that chain entirely
• A closed chain allows the next player with focus to start fresh with either card type