If Yasuo (who deals his might as damage to an enemy when he attacks) moves to a battlefield with one enemy unit that has 6 might, and Yasuo also has 6 might, does his ability kill the enemy before combat damage, allowing Yasuo to survive?

Ruling: Yes, Yasuo's "when I attack" ability resolves and kills the enemy unit before combat damage is calculated and assigned, so Yasuo will not take damage and will win the fight.

Sequence:

• Yasuo's "when I attack" ability triggers and resolves
• The ability deals damage equal to Yasuo's might to the enemy unit
• If the enemy unit is killed, no combat damage is assigned to Yasuo
• The showdown continues, allowing both players to play actions until both pass in a row
• If no new units are moved in or Yasuo isn't killed by a spell, the combat damage step is skipped and Yasuo wins

Nuances:

• The showdown phase continues even after the enemy unit is killed by the ability, so opponents can still play spells or move in additional units before combat damage would occur