Nitro-9 — Whenever Ace attacks, you may
sacrificeTo sacrifice a permanent, its controller moves it from the battlefield directly to its owner’s graveyard. A player can’t sacrifice something that isn’t a permanent, or something that’s a permanent they don’t control. Sacrificing a permanent doesn’t destroy it, so regeneration or other effects that replace destruction can’t affect this action. (CR 701.21) an artifact. When you do, put a +1/+1
counterTo counter a spell or ability is to cancel it: remove it from the stack without resolving it. A counter on an object or player is instead a marker that changes characteristics or interacts with rules or abilities; for example, a +1/+1 counter modifies a creature’s power and toughness. (CR 701.6; 122.1) on Ace, then it fights up to one target creature defending player controls.
Doctor's companionA Doctor commander may have a creature with this ability as a second commander when the deck-building condition is met. (CR 702.124) (You can have two commanders if the other is the Doctor.)