When a showdown starts and multiple attacker and defender abilities trigger, in what order do they go on the chain and who decides the order? When can players add reactions?

Ruling: When a showdown starts, all "when attacking" triggers are placed on the chain in an order chosen by the controller of those units, then all "when defending" triggers are placed on the chain in an order chosen by the defender. After triggers are arranged, the defender has priority to add reactions first (as the player who owns the top item on the chain), then the attacker can add reactions. Once both players pass without playing reactions, the chain resolves from the most recent (last) item.

Sequence:

• All "when attacking" triggers go on the chain, order chosen by attacker
• All "when defending" triggers go on the chain, order chosen by defender
• Defender has opportunity to add reactions (as owner of top chain item)
• Attacker can add reactions
• Once both players pass, chain resolves from last to first

Nuances:

• The first player able to react to items in the chain is the player that owns the top item in the chain