Knockout Maneuver

• WWizards of the Coast2025-04-04
  Official Ruling
  You can't cast Knockout Maneuver unless you choose a creature you control and a creature an opponent controls as targets.
• WWizards of the Coast2025-04-04
  Official Ruling
  If either creature is an illegal target as Knockout Maneuver resolves, the creature you control won't deal damage. If the creature you control is an illegal target, you won't put a +1/+1 counter on it even if it's still on the battlefield.

Rulings via Scryfall