Rabbid Mario is first found frozen in a block of ice in Sherbet Desert, where Toad finds him. After helping Toad get back to the center of Sherbet Desert, he uses the frozen Rabbid Mario to open a locked door, which leads to a battle with Blizzy & Sandy. Rabbid Mario falls out of the door and thaws when the battle is complete, joining the crew on their adventure.
In-game, Rabbid Mario is described as a Brawler, having high offense and mobility, but poor defense. Overall, Rabbid Mario is a very close-range fighter, as his primary weapon is a Boomshot, which deals huge damage to both enemies and allies at close range, and his secondary weapon is Melee, allowing Rabbid Mario to deal huge damage to nearby enemies with his Hammer. Unlike other heroes, Rabbid Mario has the ability to perform a 'Boom Dash', allowing Rabbid Mario to create a large area-of-effect explosion when he Dashes into an enemy, dealing large damage to all enemies and allies in the blast. His special abilities include Bodyguard, which makes Rabbid Mario take reduced damage against movement-based attacks (e.g. Dash attacks), and Magnet Dance, which forces all enemies in range to get closer to Rabbid Mario.
His Bodyguard ability can be used in conjunction with either Rabbid Luigi's Weaken ability or Princess Peach's Protection ability to decrease the damage Rabbid Mario takes from both weapon-based attacks and movement-based damage. His Magnet Dance can also be used in conjunction with " line-of-sight techniques." and his Boom Dash can also be used in conjunction with Mario's M-power to increase the damage of the said dash.