Complete the indicated task to unlock the corresponding Gladiator badge for the Arena:

Arachnobot: Awarded with the Agent of Discord badge.
Button Man Gunner: Reach level 20.
Cobra: Collect the Snake Charmer badge in Mercy Island.
Fire Thorn Caster: Reach level 30.
Juicer Sniper: Collect the Watcher On The Knoll badge in Nerva Archepelago.
Longbow Nullifier: Win one match in the Arena.
Longbow Rifleman: Collect the Locked And Loaded badge in Nerva Archepelago.
Longbow Warden 2: Complete a player vs. player mission helping your side, and another hindering your enemies.
Mook: Collect the Washed Up exploration badge in Port Oakes.
Mook Capo: Awarded with the Stone Cold badge.
Nebula Elite Buckshot: Reach level 10.
Night Haunt: Trap 50 ghosts in Fort Cerberus.
Red Hand: Trap 100 ghosts in Fort Cerberus
Wailer: Collect the Stone Keeper badge in St. Martial.