When Yasuo attacks and uses his ability to deal 6 damage to a defending Darius (5 might), does Darius die before dealing damage back to Yasuo in the showdown?

Ruling: Yes, Yasuo's attack trigger deals 6 damage to Darius before the showdown begins, killing him. Darius does not deal damage back to Yasuo because he is dead before damage assignment occurs.

Sequence:

• Yasuo moves to the battlefield
• Yasuo's attack trigger goes on the stack, dealing 6 damage to Darius (5 might), killing him
• Showdown starts
• Damage of units at the battlefield gets assigned to the other side
• Units with damage equal to their might die
• Since Darius is already dead at the damage assignment step, Yasuo only takes damage from the remaining defender

Nuances:

• You can play Reactions to the attack trigger to increase Darius's might and potentially save him from the initial 6 damage