New gamemode? Super Mario/Mayhem Boxes from Garry's Mod

SMB was a team-based sidescroller cross between Half-Life 2 and Super Mario. If it had original maps and music, there would be no copyright infringements.

It was originally called Super Mario Boxes but the name got changed to Super Mayhem Boxes when it went open-source, but it’s not on the workshop anymore, for some reason.

It could easily be a standalone game… and someone was making a free standalone version but it was cancelled.