(spoiler for episode seven in season three ig)GRR I LOVE MARKUS SEBASTIAN GRAYSON GEGGEGRgRGGRGR anyways Ima drop some lore for him : He is not one of the evil Marks but just a little mischievous and wanted to just watch the destruction of major cities that the other Marks did and actually left mid-way since he found it boring (bcs he is kind of a chaotic neutral type) and he could teleport himself to any space and time without using a portal like Angstrom and lied to him and the other Marks about his powers so the other Marks won't bother him (especially Sinister Mark, they are opps), he also knows that he is stronger than the other Marks and is in a constant moral dilemma since he has the urge to just watch while chaos unfolds while wanting to stop it, also in his world, both Debbie and Nolan died and he was raised by Cecil
(chat I'm still working on the lore :0)