Markus facts:

Markus(originally Mouse) is an experiment designed to be like Mickey Mouse. While he was the most successful out of all them, he still has problems and is very aggressive. After Boyfriend and Girlfriend get transported into his clubhouse, he seems friendly and inviting, but little do they know the bigger picture of what happened to him...

Mortimer facts:

Mortimer's(originally Suicide Mouse) look is based off of mickey mouse's original look, having bare hands instead of wearing white gloves. For the first part of misery, he's shown smiling and carrying a cart of groceries. For the second part of misery, he suddenly has a rope around his neck and a syringe jabbed in his right arm and he's now panicking. During suicide, he has a grin that is curved upwards, while still holding the groceries, the rope as well the syringe in his hand, his pupils are also melting, during happy ride, his eyeballs have popped out of their sockets and dangling in front of his face by their optic nerves, his grin also gotten wider. In the first half of insanity psychosis, Mortimer is sitting on his knees in a slightly slumped position with his mouth wife open and stretched wide. His eyes have fallen out of their sockets and are now bouncing on the palms of his hands, while black liquid(most likely blood) leaks out if the sockets. Some of his teeth appear to be missing when compared to his appearance in happy ride, he also no longer has his groceries basket he had prior the three songs. During the second half of insanity psychosis he gets back up, his eyes are back in his sockets and he's wearing gloves, but now his mouth is melting and open wide in an unnerving smile, and walking with a syringe in his left hand.

More facts here: https://fridaynightfunking.fandom.com/wiki/Vs._Mouse#3.0_Alpha