If Yasuo attacks and his trigger goes on the stack, can the opponent use Rebuke during the showdown to remove Yasuo and prevent his ability from KOing the target?

Ruling: Rebuke cannot be played while Yasuo's trigger is on the chain because Rebuke is Action speed and cannot be played to a closed state (ongoing chain).

Nuances:

• If Yasuo is removed from the battlefield at Reaction speed while his When I Attack trigger is still on the chain, the trigger will still resolve but will be unable to hit its target because the target is no longer at the same location as Yasuo.