This is a lot of incarcerated supervillians to take in, I realize.  In the first panel, from left to right, they are:

Beetle Bandit
The Maw
Professor Brainfever (from Chris Morse’s excellent Supervillain Corner podcast)
Mantis Man
Uniscorn
Cyberback
Big Idea
Dr. Devil
Zoot Suit Brute
Raveneer
Bulls McCoy
Punkbot 9000
Big Papa (also from Supervillain Corner)
Question Shark
Sir Ringe
Batnick
Hammerhead
Jack (a soldier of fortune with a bionic arm, from one of J.R.’s Dr. Mercury stories)
Cockroach
Mickey Fin
Laser Mind
Cy-Boar
Secret Toad
Scream Shovel
Gnome Bros

Panel 2 has Cockroach getting grub with Headcannon, and that’s Sir Ringe again in the background.

Cockroach seems to have made an enemy of Rock Lobster in panel three. That’s Jack in Cockroach’s corner, and Cyberback behind the both of them.