If Volibear attacks a unit at Reavers Row and the defender uses Reavers Row's effect to retreat, does Volibear's 5 damage still apply to that unit?

Ruling: No, the damage does not apply to the retreated unit. When Volibear's attack trigger resolves, if the targeted unit has been moved back to base, it is no longer a valid target and receives no damage.

Sequence:

• Volibear moves to the battlefield, triggering combat
• Attacker and defender designations are assigned when the showdown opens
• Volibear's attack trigger goes on the chain first, and targets must be chosen at this time
• Reavers Row's defender trigger goes on the chain second (on top)
• If both players pass priority, Reavers Row resolves first, moving the unit back to base
• Then Volibear's trigger resolves, but the retreated unit is no longer a valid target and takes no damage

Nuances:

• When splitting damage among multiple targets, you must choose all targets when the trigger is finalized on the chain, before the defender can react
• Each target must receive at least 1 damage (you cannot assign 0 damage to some targets)
• Choosing multiple targets is strategically better because if one is retreated, you can still assign damage to the remaining valid targets
• Units do not become attackers during movement - they gain attacker designation when the showdown opens, which happens after movement resolves
• If a unit is revealed from hidden after targets are chosen (like Teemo), it cannot be targeted by Volibear's trigger