Protocol Knight is a common Creature — Human Knight card from March of the Machine (MOM), collector number 74. Current market price: $0.23 (foil $0.19), TCGplayer market prices via Scryfall.
When this creature enters, tap target creature an opponent controls. Put a stun counter on that creature if you control another Knight. (If a permanent with a stun counter would become untapped, remove one from it instead.)