Mace Knight is one of the Meta-Knights who serve under Meta Knight himself. He dons purple armor, like his counterparts, with golden shoulder pads and blue shoes. He carries around a flail nearly as big as himself, holding it by the chain.
Mace Knight gangs up on Kirby with the rest of the Meta Knights, appearing as a recurring mid-boss. Meta Knight gives the command upon seeing Kirby, then vanishes, as Mace Knight and the others appear in a surprise attack. Mace Knight swings his flail over his head a few times before thrusting it forward. Then he takes a few steps and repeats. Sometimes, he will swing his flail early if Kirby gets too close. Occasionally, upon spawning, Mace Knight will swing his flail over his head crazily as he dashes across the room. Upon reaching the end, he turns around and proceeds.
Mace Knight behaves in the same way as before, but slightly more independent; he spawns without waiting for a command. His attacks are the same, as well.
Mace Knight is also a key character in Revenge of Meta Knight, having his own dialogue throughout the subgame. He is one of the crew-members that watches as Kirby gradually wrecks the battleship Halberd. Despite his witty conversations with others, he also attempts to stop Kirby as he approaches the room where he will encounter Meta Knight, accompanied by others.
His role as a crewman of the Halberd is watching the radar for any suspicious objects; it is shown in one of the conversations with the crew when Kirby disappears into the secret room of the clouds, with the line, "Ack! Kirby's disappeared from the radar!" Strangely, in the Meta Knightmare Ultra credits, he isn't seen with Captain Vul, Axe Knight, Sailor Waddle Dee, and Meta Knight in a screenshot with the Halberd crew or in the opening credits.
On the Halberd, there is a secret room containing a secret stash of food and 1UPs. If succeeding in finding the room, he accidentally notifies his superiors about the secret stash. Kirby can proceed to replenish himself with this, much to his dismay.