Hmmm... I have a few traits, but I don't think enough to be a Mary Sue.
Cal has had a traumatizing event in his past, but he hates everyone, and everyone hates him, basically :P And otherwise he's a pretty normal Intern, really.
Ricky's a genius by Slig standards, but he's as mean and heartless as any slig, really.
Murphy... he's absolutely deranged, nobody really knows much about his past, and he's got a seemingly endless supply of explosive equipment. But he doesn't talk (properly, anyway, it's just babbling) and he's very active and energetic for a Clakker (look out Cal
)
Wic's a Mudokon who was just found out on the streets by Cal. Everyone presumes he's 'freed', he somehow found his way out of the nursury he was hatched at (probably with the help of an older escapee) and has been wandering ever since. He's young, sweet and naive, but also strong-willed and clever.
Barnabus... pretty much your average Big Bro Slig. Big, strong, stupid, likes guns, there we go.
Marvak is a Chief Mudokon, founder of a tribe, and he never was enslaved by the Industrialists. Stubborn, determined, physically strong and has a few Shamanistic powers.
Veleno... he's the Glukkon in charge of an army camp. Shrewd, mean, notices everything. The word 'veleno' means 'poison' in italian
how nice.
Zozo, I suppose you could add something about a characters mysterious or unknown past, if they have amnesia, etc. And maybe if that character's an extinct/nearly extinct species (Meech, Gabbit, Steef etc.)