Supervillains are as you expect: Superpowered people who use their powers to commit crimes and most likely strike it rich. There are multiple different supervillain organizations such as The Dream SMP, The Eggpire, and Las Nevadas Enterprises. But there are still a plethora of supervillains out there.

Supervillains (in organizations and not) include but are not limited to:

Dream-with the powers of super strength and energy manipulation Dream wields no Power Weapon

GNF/GeorgeNotFound-the mushroom on his head actually is a part of his and release sleep inducing spores so GNF isn't on the field much so he has no power weapon

SapNap-with his power of fire manipulation SapNap still needs special gauntlets to make sure he doesn't burn his hands

Quackity-Quackity's only real superpower is his wings that really act more as speed enhancers so a shotgun as his Power Weapon helps him out in combat

BadBoyHalo-his power of shadow manipulation make him quite the opponent when night falls and he doesn't use a Power Weapon

The Arachnid-her power of manipulation through her energy webs of red-wine color energy silk that match her hair, eyes, and leggings her powers are hard to counter and wielding a sword as her Power Weapon with two pistol's at her waist she's quite the woman to fear

The Chameleon-not born with his powers of shapeshifting instead given to him from experimentation from scientists trying to turn him into a copy of Enderian from the L'manberg Organization but instead turned him into a shapeshifting near failure and now he's a thief for hire with a pair of daggers as his Power Weapon

So there are a few of the supervillains of the city.