Roid Rage Psycho

The Roid Rage Psycho is a creature that was created by a vicious enemy named Sledge.

Involvement
The Roid Rage Psycho is seen during the main story quest in Sledge's Safe House that requires you to collect Sledge's Mine Key. At the end on the inside of the building, it is a semi-large round room that the key is located. The creature will be located at the end of the room and start to attack you, along with lots of Midget Psychos. Defeat the Roid Rage Psycho in order to collect the Mine Key.

General Strategy
This enemy attacks in 2 ways, the first being a traditional melee attack which causes large amount of damage. The second is a ranged attack in which a grenade with an Explosive MIRV mod is thrown. Alongside the Roid Rage Psycho, there are lots of Midget Psychos attacking you once you commence the battle. (Recommended to do this boss in Co-Op). It is possible to defeat this boss without getting damaged by his melee attack by going in the back of the round room (the way you came from) and go into a hole where there is a fence in front. This circumvents the melee attack's damage, but not the grenade attack. Bullets will NOT go through the fence, but if you have a weapon called T.K.'s Wave, obtained from the quest T.K.'s Life And Limb, the plasma shots will go through the fence and cause damage. There is also a small gap between the fence and the railing the fence is attached to, allowing you to get critical headshots with a sniper rifle from a place of relative safety. You can get out of the hole at any time and come back in while attacking with other weapons. The Roid Rage Psycho has no shields, but a large amount of health. This and its size make the fight a little complicated.

Due to his large size, getting critical headshots is quite easy and makes the fight much easier. If you are taken down, the easiest way to get second wind is to kill one of the many midget psychos, which can be easily done using a shotgun to the head as they will run up to you while downed.

Specific Strategies/Tips

 * As the soldier, you can distract him by deploying your turret which he will attack until both the shield and cannon has been destroyed. While he is attacking the turret, it is easy to sneak in some critical headshots with a sniper rifle from afar. Before doing this you should try and get rid of the midgets by using your combat rifle, since they will chase you around and become a nuisance when you are trying to distract the Roid Rage Psycho with the turret.
 * It's possible to wallclimb directly to the left of the entrance. Once on the wall he'll consider you 'unreachable' and stand still while you pump rounds into him. Eventually he'll use a grenade, and you'll need to sprint away, but you can just climb back up after the grenades detonate. In co-op it's handy to have a person who holds aggro well do this since it renders his melee attack harmless (he won't run after the other players), as well as holding him still and making him an easier target.
 * As the Siren, the easiest way to kill the Roid Rage Psycho is to find a quick-reload SMG, then back away from him as you pump critical hits into his head. If your shields go down, activate Phase immediately, then run to the other side of the room and continue. IMPORTANT: DO NOT ATTACK MIDGET PSYCHOS unless you are in last stand. as long as you keep moving, they are unlikely to do any damage to you. Remember, the Roid Rage Psycho is slower than you, so backing away is key. If you feel like he is getting too close, you can simply turn and sprint away.
 * There is a very easy way to defeat the Roid Rage psycho. When in the small pit at the entrance to the boss room hop up on the platform on the right. Do not enter the room itself. The fence has a small gap that you can aim through at the right hand side. You can snipe the midget psychos on the right hand side (who will be throwing axes) and the Roid Rage Psycho from there. If you do not enter the main area of that room the Roid Rage Psycho won't move, making headshots simple to line up. This has been confirmed on all platforms.
 * Another useful trick is to get him into the hole. He can't hit you when he's in there, and the fence prevents his grenades from hitting you. The midgets can be killed first. Even better- His items will be all neat and together!
 * Also, although the main fence between you and the arena cannot be shot through, the two fences before the main area can, so you can provoke the Psychos out and Grenade Jump behind the fences and snipe them, while their buzz saw throwing will not reach you.