Mainframe appears in Season 2, episode 18 'Wheels of Fury' as an Artificial Intelligence created by Tony Stark to play games against. Iron Man, Hulk and gang end up in a high stakes game of Roller Derby against Mainframe. At the conclusion of the episode, Mainframe determines that humanity has many games to offer, taking on a familiar armored form similar to his MC2 design and setting out to discover the world.
I don't really have a strong opinion about the series, as this was the only episode I've ever seen. My interest is certainly piqued by the use of a MC2 character in animated form, considering May 'Mayday' Parker was passed up for the derivative gender-swapped 'Petra Parker' in the Ultimate Spider-Man animated series.
Until the entire MC2 makes an appearance in another medium, I remain
frogoat