How many chains can occur during a showdown, and can you play actions after your opponent plays a reaction?

Ruling: You can have as many chains as you want during a showdown. The showdown only moves to damage calculation when the chain is empty and both players pass priority back to back consecutively.

Sequence:

• Player initiates showdown (e.g., moves unit to contest battlefield)
• Players can play actions and reactions, building a chain
• When chain resolves and is empty, players can start new chains
• Only when the chain is empty AND both players pass consecutively does damage calculation occur

Nuances:

• After an opponent plays a reaction on the current chain, you can only add reactions to that chain
• However, once that chain resolves, you can start a new chain with actions before damage calculation