If an opponent attacks a battlefield I control, and they pass priority, and I pass priority, do they get another priority opportunity?
No, the attacker does not get another priority opportunity.
According to the rules of a showdown, the showdown ends immediately once both players pass priority in succession without adding any new items to the chain.
Sequence of events:
- Attacker passes priority: The attacker chooses not to play an action or reaction.
- Defender passes priority: The defender also chooses not to play an action or reaction.
- Showdown ends: Because both players have passed priority consecutively while the chain is empty, the showdown concludes immediately. No further actions or reactions can be played, and the game proceeds to combat damage resolution.
As stated in the FAQ: "Once both players pass priority in order during a showdown, the showdown ends. The attacker cannot open a new chain after both players have passed."