As I mentioned in my review, characters in The Vigilante Hack are supposed to be regular folks like you and me, pushed into the rolls of vigilante. The characters do not have super powers. That being said, the setting has some things out of the ordinary (just look at the sample villains). I think that you could create something a little out of the ordinary, like let's say a Teenage Mutant Ninja Turtle, and still fit into the world of The Vigilante Hack. Here's my little TMNT Hack for The Vigilante Hack.
A mutant turtle character is created as usual, but also has the following features. It can hold its breathe underwater for 10 minutes, gains advantage on swim-related checks, and is always considered to be wearing light armor when attacked from behind. However like regular armor, this only protects them from 2 points of damage, until they rest. Due to its appearance it suffers disadvantage on all social rolls other than intimidate.
As you can see these doesn't do anything drastic mechanically and still fits the gritty vibe of the game. You can alter this slightly to include other mutant characters to your game.