In a showdown does the attacker or defender pass priority first?

In a showdown, the attacker receives priority first.

According to the established rules and FAQs for Riftbound:

1. Initial Priority: When a showdown begins, the attacker gains focus and priority first (Rule 341, Rule 442.1.a.1.a).
2. Initial Chain: If an "Initial Chain" of attack/defend triggers is created, the attacker retains priority to react to those triggers first (FAQ #4575).
3. Focus and Priority: After the initial chain resolves, the attacker retains focus and priority (Rule 343.1, FAQ #4575).
4. Passing Priority: Once the initial chain is complete and the state is open, focus and priority alternate between players. If the attacker passes priority without playing a card, the defender then gains the opportunity to play an action or reaction (FAQ #6977).

Summary of Priority Flow:

• Attacker has first priority.
• If the attacker passes, priority moves to the defender.
• If the defender plays a reaction, priority returns to the attacker after that reaction resolves (FAQ #5067).
• Priority continues to alternate between the attacker and defender until both players pass consecutively, at which point the showdown closes (FAQ #5067, Rule 345).