When Anivia attacks into Yi and First Mate defending together, and Anivia deals 3 damage to First Mate, what is the sequence of effects and does First Mate survive?

Ruling: First Mate dies and then Yi becomes 8 might.

Sequence:

• Anivia's "when attacking" trigger goes on the chain
• Yi's "while defending alone" ability would trigger and go on the chain after
• Chain resolves backwards: Anivia deals 3 damage to First Mate first
• First Mate (3 might) dies from the 3 damage
• Yi's ability then applies, making Yi 8 might (since he's now defending alone)

Nuances:

• Yi's ability is worded as "while" but still uses the chain/trigger system rather than being a passive static effect
• The key is that Anivia's damage resolves before Yi's "defending alone" bonus applies