First encountered during a typical, moonlit, samurai rooftop duel in Onimusha: Warlords, Marcellus is a minor foil to Samanosuke Akeche. He wears the same gauntlet on his arm as the game's hero, but is clearly under demon control. After defeating him the first time, players will gain Marcellus' wind orb which takes the form of the Shippu (a double-bladed-staff), completing the trifecta of Oni weapons they collect in the game. The Shippu's special attack is largely the same as Marcellus' wind attack. Though seemingly destroyed on the roof, he is summoned again by demon scientist Guildenstern to do combat with Samanosuke before the arrival of the game's final boss, Fortinbras.
In this second battle Marcellus will progress through a series of phases based on the weapons he carries. He begins with a sword and shield; once the shield is destroyed, his second and more dangerous weapons, a set of katar, are revealed. In Warlords, Marcellus is generally a fast moving enemy who needs to be blocked constantly; his appearance in the third game of the series is markedly different, with Marcellus taking on a slower, damage-heavy approach. Again, he appears twice in the game before finally being "defeated," if such a thing is even possible with a character who habitually returns to life.
Blade Warriors allows players to take control of three different versions of Marcellus once they have unlocked them: normal Marcellus, Power Marcellus and Speed Marcellus.