This medallion is known to the CWCki as the Mark IV, and we are viewing its reverse side. The obverse is more recognizable as a grimy Sonichu. It is the medallion Chris was wearing when he was arrested, and he has had it for several years. It languished in a storage locker at the jail during Chris's stay there, but has now been returned to him.
Medallions are made from Crayola Fuckin' Model Magic and painted with acrylic paint. Due to the porous nature of the materials used, they accumulate grime, and I think Chris tried to mitigate this by coating the Mark IV in sealant, perhaps improperly mixed. Chris wears the medallions in the shower, so much of the grime comes from soap scum, Chris's shed skin cells, and sweat.
The cyclopic object in the center of this side of the medallion is a magic stone. Adding such a stone to a medallion makes it a Megastone medallion. Chris became interested in crystal magic around 2018 and it fits in with his New Age beliefs. You can see he's wearing other such stones, but it's easy to miss them because the Mark IV just steals the show.
To the left of the stone, you can see the remains of a Sonichu sticker. You kind of have to know what Sonichu is shaped like to see it. To the right of the stone, there is another sticker, I think some sort of special pokeball. This is thoroughly covered in globs of sealant, with the aforementioned grime filling in the nooks and crannies.
Chris has recently been spotted with a Mark V medallion which is not so worn out and looks like the ones Praetor was selling.