Gremlin Markus is a Gremlin who works on Mean Street.
He is Gus' nephew, shown by calling him "Uncle Gus" when you meet him. After introductions are made, Markus helps Mickey activate the Projector Screen to OsTown, then the Screens to Tomorrow City, Ventureland, and Bog Easy. He tells Mickey what each Screen needs to be activated and how much of it is needed, even giving him advice. For example, Markus tells Mickey the locations of the Gears to power the Screen to OsTown, as well as two possible solutions to obtain a Power Spark. Every time Mickey brings Markus the correct number of Power Sparks, the Gremlin happily sets to work.
After Mickey returns from Tomorrow City, three Spatters capture Markus in a Gremlin Cage. However, since Markus' freedom is required for the story to continue, he doesn't count for the Gremlin Guardian Pin.
After Mickey returns from Ventureland, Markus finds a stash of three Power Sparks, but three Bunny Children come along and steal them. Markus tells Mickey to get them back.
After Mickey returns from Bog Easy, Markus finds a hidden section in the Projector Screen machine connected to the Fire Station. After Mickey gives Markus 30 Power Sparks, Markus activates this special section to reveal Walt's Apartment.
- According to Markus, Gremlins mostly avoid going to areas like Tortooga and Lonesome Manor, where there's not much technology. Sure, there are still trapped Gremlins in those areas, but only three in the former and seven in the latter, compared to nine in the technology-packed Tomorrow City.
- After Walt's Apartment has been revealed, Markus says that he would like to go to a theme park and have some fun sometime, despite the fact that he lives in a theme park.