*Metallix (pronounced "Meh-TAL-licks"), originally known as Metal Sonic, is a major antagonist in Super Mario Bros. Z, and the main antagonist of the Metallix Saga. He is an evil, ultra high-performance super-robot who seeks the Chaos Emeralds to complete his power.

Metallix teleported from Sonic's World to the dimension of the Mushroom Kingdom. When he landed, he noticed a nearby Goomba holding the Blue Chaos Emerald. Metallix demanded the Goomba give him the Chaos Emerald. When the confused and terrified Goomba didn't know what he was talking about, Metallix destroyed him with a single blast.

Metallix later looked over the wilderness of the Mushroom Kingdom, observing his Chaos Emerald. After contemplating his next move, he took off into the distance.

Metallix later fires a set of missiles at Luigi and Yoshi, who are fighting Wario and Waluigi over the White Chaos Emerald, sending Wario Bros. blasting off and causing Yoshi to fall into deep into the Grassland's forest. Metallix arrives and demands the Chaos Emerald from him. Yoshi refuses to hand the Emerald over, earning Metallix's ire and prompting him to attack.

Yoshi is punched and sent flying through several trees before crashing into the wall of a plateau. He gets up quick enough to watch Metallix trying to retrieve the Chaos Emerald. Using his tongue, Yoshi snatches the Emerald before Metallix does, and places it in his mouth. Metallix demands Yoshi to spit the Chaos Emerald out.

Despite having his life threatened, Yoshi boldly swallows the Emerald and belches in Metallix's face. Amused, but unfazed, Metallix decides to simply kill Yoshi and take the Chaos Emerald from his 'mutilated carcass'. Yoshi then uses his Egg Roll and escapes as he is hounded by an onslaught of bullets from Metallix's arm-mounted mini gun.

He barely manages to escape the line of Metallix's mini gun fire. However, Metallix fires four missiles from his missile launcher on his shoulder, with the missiles striking Yoshi in his Egg Roll.*