Gladiator is a new feature to the Arena in City of Villains, where you unlock and do battle with various NPCs from throughout the game. To unlock them you must do certain things, such as defeat #X of them, gather a certain exploration badge, etc. The name of the badge is the name of the NPC it unlocks.
Complete a PvP mission helping your side, and one hindering the enemies.
Longbow Rifleman
Find the Locked and Loaded badge in Nerva Archepelago.
Cobra
Find the Snake Charmer badge in Mercy Island.
Wailer
Find the Stone Keeper badge in St. Martial.
Mook
Find the Washed Up exploration badge in Port Oakes.
Juicer Sniper
Get the Watcher on the Knoll badge in Nerva Archepelago.
Arachnobot
Gotten along with the Agent of Discord badge.
Mook Capo
Gotten along with the Stone Cold badge.
Nebula Elite Buckshot
Level up to level 10.
Button Man Gunner
Level up to level 20.
Fire Thorn Caster
Level up to level 30.
Red Hand
Trap 100 ghosts in Fort Cerberus
Night Haunt
Trap 50 ghosts in Fort Cerberus.
Longbow Nullifier
Win one match in the Arena.
11/3/2005
Supergroup Badges
Supergroup badges are badges you get for doing certain tasks while in supergoup mode. They unlock items that can then placed in your base. Some need to be crafted, some you can just purchase. SG badge progress is shared by all members of the SG, so to unlock the Analyzer Base Defense for example, you could have 2 members take 10 million points of damage each. To check your SG badge progress, open your badge window and press the "SG Badges" button.