If Yasuo is moved to a battlefield (triggering his on-attack ability), then moved to base before it resolves, then moved back to the same battlefield in the same combat, does his on-attack ability trigger a second time?

Ruling: No. On-attack abilities trigger when a unit is declared as an attacker for the first time in a combat. Moving the same Yasuo out and back in during the same combat does not trigger the ability again.

Nuances:

• Yasuo can trigger multiple times per turn, but not per combat
• If Yasuo is moved out after his trigger resolves and combat completes, then moved back in for a new combat in the same turn, the ability would trigger again
• Moving in a second (different) Yasuo would trigger that unit's on-attack ability
• Units are considered one entity in themselves