|“||Now let's see what's happening with this device...||”|
–Gremlin Markus, Epic Mickey
He's 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. 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.
- Apart from Gus, Markus is the gremlin with the most appearances in the first game, making it ironic that he was not in the second.
- 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.
- Although he could be meaning that he wants to go to a theme park that ISN'T dark and twisted.
- Markus does not appear in Epic Mickey 2: The Power of Two. He is instead replaced by his cousin, Jamface, who is identical to Markus in appearance. According to Gus in Dark Beauty Castle, Markus was squashed by an operating table during an earthquake and had to have somebody fill in for him. It is possible that when the Mad Doctor sings, "Help Me, Help You" at the beginining of the game, he appears as the song takes place right when the quakes start. However, he makes no confirmed appearance at any point.
- Looking deep into the files of Epic Mickey 2: The Power of Two some of the files for Jamface are named Gremlin Markus. Reason for that is, that originally Markus was meant to appear again, but got replaced by Gremlin Jamface later in development. This also would explain why both look exactly the same.