During a showdown with both 'when I attack' and 'when I defend' effects, who gets priority first to play reactions, and how does priority work on the chain?

Ruling: During the initial chain of a showdown, when both 'when I attack' and 'when I defend' effects go on the chain, the defender gets priority first to play reactions because their 'when I defend' effect goes on the chain last (making it the topmost item). The player controlling the topmost item on the chain always gets priority first.

Sequence:

• When a showdown begins, 'when I attack' effects go on the chain first, then 'when I defend' effects
• The defender (controlling the topmost item) gets priority first and can play as many reactions as they want before passing
• Once they pass, the attacker can play as many reactions as they want, then passes
• Players alternate passing until both pass in a row, then the topmost item resolves
• After an item resolves, whoever controls the new topmost item gets priority again
• This continues until the entire chain resolves
• Once the chain fully resolves, focus passes automatically to the other player

Nuances:

• Reactions don't necessarily target the top of the chain - they can target any legal target on the chain or even something unrelated
• A player with priority can play multiple reactions in a row before passing, but the opponent's reactions will still resolve first (since they go on top of the chain)
• Priority works this way for all chains, not just the initial showdown chain
• Focus (for playing actions) passes automatically after a chain resolves, unlike priority which requires passing
• Optional 'when defending' effects (like battlefield abilities) still count as going on the initial chain even if you choose not to use them