Mari-Robo's debut appearence is in the 2017 game Mario & Yoshi: Mushroom Kingdom Heroes. He first appears as the boss of World 4, Geartropolis. According to the Gearmos in the city, Mari-Robo has been dictating them so they could make traps in the factory he rests in to keep Mario and Yoshi from getting the 5th Star Key. During the fight against him, Mari-robo flies around the arena, shooting cannon blasts and occasionally throwing bombs at the duo. To defeat him, Mario must pick up the bombs (or Yoshi can eat the bombs) and throw them at the robot. Mario can also just use his own bombs as Bomb Mario to defeat him. Once that is repeated 4 times, Mari-Robo starts malfunctioning and falls off the stage, dropping the Star Key.
At the end, when the book turns to the page for World 4, Mari-Robo is seen badly damaged, with Gearmos celebrting around him.
Mari-Robo greatly resembles Mario, with a few notable differences. His "skin" is metal-colored, his shirt and cap are darker than Mario's red, his overalls are grey, and his gloves are grey as well. He also has an arm cannon, which he uses to shoot fireballs, and has a jetpack as well. Mari-Robo can throw bombs, as one of his most notable abilities, since it is key to defeating him in his first appearance. He appears to be made of metal, as if Mario tries to jump on him, he bounces off with a metallic "clank" noise. Mari-Robo's original appearance gave him black overalls, grey "skin", and an entirely black jetpack, as opposed to grey and gold. His arm cannon lacked his emblem, and was black as well.
Mario & Yoshi: Mushroom Kingdom Heroes Beta sprite