Not what I was expecting but honestly seems like a pretty funny idea.
Regarding Chell and the Syndicate, part of the coming post is a character who I made close to a month ago now.
Deran, a bounty hunter who takes jobs for both the law and crime rings alike. He's worked both with and against Chell in the past, developing a sort of one-sided rivalry. He sees her as a sort of acquaintance though doesn't get very far given her more stoic nature.
As for the latter idea, I actually already had two characters in the works. A loan shark mob boss (an existing character of mine I'd shelved) to serve as a villain/boss character. He's only existed in text form as I haven't drawn him yet, but he also has a mostly complete move set as he was intended for a previous platfighter idea too.
The other is still just a basic concept, being a true villainess character to fulfill the role of the ruthless huntress/femme fatale/assassin style character. I'll definitely try using the animals you listed to play around with her design. Makes for an interesting direction overall from what I was originally looking toward.
Given the cowboy/stockman-based design on Chell, over time I wound up envisioning her as a more heroic sort of character though still in the grey overall given her profession. Sort of anti-hero-like in a way. You could say Chell is like a slightly softer version of The Man With No Name while Deran is like a more brash Han Solo.