Quest: You. Will. Die. (Seriously)
Appointed By: Tannis
If you beat Borderlands 2 Playthrough 1 and Playthrough 2 / 2.5 and are tired of wandering around in Vault Hunter mode, then you may be looking for a challenge and a way to farm good loot (especially if preparing for future DLC battles).
Fighting the Borderlands 2 boss - Terramorphous the Invincible - is a great way to go!
This Thresher boss is located in Thousand Cuts. It costs 4 Eridium to fight this boss. He's harder than Crawmerax from Borderlands 1 - The Secret Armory of General Knoxx - and a bit weaker than the more secretive and elusive Vermivorous The Invincible.
You can solo him, duo / co-op him, or fight him in a bigger party of three or four. His difficulty will scale up with more party members in your group though.
When killing him, he drops awesome rare, epic, and legendary loot. So load up on class mods, grenade mods, guns, shields,
and artifacts / relics.
There is no class that cannot kill this beast of a thresher.
Axton the Commando / Commander / Soldier can do it -- and his turrets are a great distraction against the boss (plus provides a shield for you and your allies)
Zer0 / Zero the Assassin -- with his powerful sniping and his stealth capabilities, he is powerful during this battle
Salvador the Gunzerker -- With two guns, he can shower Terramorphous the Invincible with bullets for high DPS / damage per second
Gaige the Mechromancer -- Similar to Axton, her robot Death Trap will be a good distraction & support during this battle
Maya the Siren -- By far the MVP for this particular scenario, Maya can heal her allies AND resurrect them with Phaselock while also attacking with elemental weapons
How to Kill Terramorphous the Invincible
1) Dodge the rocks he throws (they cause area damage though so be careful)
2) Distract him when possible with skills and friends
3) When he uses Beam Tentacles, hide behind the nearby rocks
4) Use a fire resistant shield to protect against his fire / pyro form
5) Hide behind rocks when he tries sucking everyone up as a black hole thresher
6) Optional, but again you may want to have a Siren help you
It is recommended that you use the Best Borderlands 2 Shield -- The Bee -- and join that with the Best Borderlands 2 Gun -- Conference Call. You'll do MASSIVE amp damage and kill that boss more easily with an extremely high rate of DPS / damage per second.
Once you get lots of good loot, you can actually farm Terramorphous the Invincible easily. That's when you'll want to encounter the even harder boss...Vermivorous The Invincible! FYI you'll also get the Blood of Terramorphous.
Terramorphous Rock Glitch
You can actually use a glitch to fight the boss very easily. It works so well that you can even solo the monster without needing any help or people to distract the master boss. When on the platform, move to the right and try to get by a tiny ledge that's by a rock.
When hiding here, you can hit Terramorphous, but he is unable to hit you with all his tentacle attacks EXCEPT for rock hurling. When he does this attack, be careful, as you can get hit and fly off the map.