A raid boss is a specialized boss which is designed to be fought by multiple players, typically of significantly higher difficulty than normal bosses and requiring specialized strategy and/or loadouts. Within Borderlands, Borderlands 2 and Borderlands: The Pre-Sequel, raid bosses have the title "the Invincible," are optional encounters, and need not be defeated or even fought to complete their respective main stories. However, some of them must be defeated to complete the achievement/trophy lists for their respective content.
Originally, Borderlands lacked anything which could be considered a true raid boss. All bosses, even optional encounters, were designed such that single players could defeat them. The first raid boss to appear in the Borderlands series was added by a DLC, The Secret Armory of General Knoxx. The optional mission You. Will. Die. tasked players with defeating the appropriately named Crawmerax the Invincible. Though not specifically designed to be unkillable by a single player, Crawmerax's high difficulty coupled with hard-to-hit vulnerable spots, particularly the one located on its back, made him effectively off-limits to most solo players.
On its release, Borderlands 2 was advertised specifically as having a specially designed raid boss meant to be fought by four level 50 characters. The boss, Terramorphous the Invincible, was inspired by Crawmerax and meant to be more difficult than him. Much of the design of Terramorphous references Crawmerax, including the arena used for the fight as well as the mission name: You. Will. Die. (Seriously.). Entering Terramorphous Peak, where Terramorphous is fought, requires a payment of eight Eridium.
A second, somewhat hidden raid boss was also included. Vermivorous the Invincible is the most advanced metamorphosis that a varkid can reach. Though it can theoretically be encountered at any level and with any number of players on True or Ultimate Vault Hunter Mode (it cannot spawn on Normal Mode), the chance of a varkid progressing through the necessary metamorphoses is highest with four level 80 characters. Vermivorous also has health far in excess of Terramorphous, estimated at around 200% of Terramorphous's health.
The DLCs for Borderlands 2 have also included a large number of raid bosses. To date, all story DLCs and one of the five Headhunter Packs have included at least one raid boss. Accessing the DLC raid bosses requires a payment of eight Eridium, except for the Ancient Dragons of Destruction, The Invincible Son of Crawmerax the Invincible and Haderax the Invincible, who require 20, and Dexiduous the Invincible who requires between 95 and 99.
Captain Scarlett and Her Pirate's Booty
The first story DLC, Captain Scarlett and Her Pirate's Booty, introduced two new raid bosses, available after completing the DLC's story missions. The first, Hyperius the Invincible, is a Hyperion Engineer who has "gone mad with power" and was granted Seraph Guardian status. The second, Master Gee the Invincible, is another Seraph Guardian of unknown origin who fights the Vault Hunters alongside a collection of Sand Worms. A third raid boss (or bosses), the offspring of existing DLC boss Roscoe, was planned but ultimately not included.
Mr. Torgue's Campaign of Carnage
The second story DLC, Mr. Torgue's Campaign of Carnage, adds a third raid boss, Pete the Invincible. Pete is an upgraded version of an earlier standard boss, Pyro Pete, who has been enhanced with both fire and corrosive attacks, as well as extremely high health. Like the previous two DLC raid bosses, Pete is a Seraph Guardian and will drop Seraph Crystals.
Sir Hammerlock's Big Game Hunt
The third story DLC, Sir Hammerlock's Big Game Hunt, adds two raid bosses: Voracidous the Invincible and Dexiduous the Invincible. The former is a Seraph Guardian stalker controlled by a savage chieftain; the latter is an enormous Wetland Drifter. Dexiduous holds the record for the highest Eridium cost of any raid boss, and is the only raid boss alongside Vermivorous to be battled outside of a dedicated arena.
Tiny Tina's Assault on Dragon Keep
The fourth story DLC, Tiny Tina's Assault on Dragon Keep, adds new raid bosses known as the Ancient Dragons of Destruction, that consists of four Seraph Guardian dragons: Boost the Invincible (slag), Incinerator the Invincible (incendiary), Healianth the Invincible (shock), and Brood the Invincible (corrosive). They can be found in a secret area named The Winged Storm, accessed by putting 20 Eridium in a stone bowl outside of its hidden entrance in Lair of Infinite Agony. None of the dragons will drop any loot until all four are killed, where their loot will erupt in a geyser out of the centre of the arena.
Sir Hammerlock vs. the Son of Crawmerax
The fifth Headhunter DLC, Sir Hammerlock vs. the Son of Crawmerax, adds one raid boss in the form of the colossal craboid, The Invincible Son of Crawmerax the Invincible. A more powerful version of the Son of Crawmerax fought during the Headhunter's story, the Invincible Son can be summoned by returning to his arena and placing 20 Eridium into a basin just outside its lair. Unlike other raid bosses, The Invincible Son does not have any dedicated loot drops, but killing it grants access to an otherwise inaccessible treasure room containing seven chests that have a higher than average chance of containing legendary or pearlescent gear.
Commander Lilith & the Fight for Sanctuary
The fifth story DLC, Commander Lilith & the Fight for Sanctuary, adds one raid boss in the form of Haderax the Invincible. Haderax is a colossal, purple Sand Worm that can be summoned by entering Writhing Deep after the DLC's story is complete, accessing the elevator against the northern wall of the cave, placing five Eridium each into the four receptacles (totaling 20 Eridium) and then pressing the button to prompt a 'sonic drop'. Haderax is one of two story DLC raid bosses (the other being Dexiduous) who is not a Seraph Guardian, though it is the only raid boss capable of dropping effervescent gear.
Full List of Raid Bosses in Borderlands 2
|S. No.||Raid Boss||DLC||Species||Mode||Seraph|
|1||Terramorphous the Invincible||main game||Thresher||52||52||92||8|
|2||Vermivorous the Invincible||main game||Varkid||N/A||52||93||0|
|3||Hyperius the Invincible||Pirate's Booty||Engineer||32||52||92||Yes||8|
|4||Master Gee the Invincible||Pirate's Booty||Sand Pirate||32||52||92||Yes||8|
|5||Pete the Invincible||Campaign of Carnage||Biker||32||52||92||Yes||8|
|6||Voracidous the Invincible||Hammerlock's Hunt||Stalker||37||52||92||Yes||8|
|7||Dexiduous the Invincible||Hammerlock's Hunt||Wetland Drifter||38||53||93||90-99|
|8||Ancient Dragons of Destruction||Dragon Keep||Dragons||37+||52+||90+||Yes||20|
|9||The Invincible Son of Crawmerax the Invincible||Son of Crawmerax||Craboid||37||52||92||20|
|10||Haderax the Invincible||Fight for Sanctuary||Sand Worm||38||52||92||20|
Borderlands: The Pre-Sequel
The only raid boss present in Borderlands: The Pre-Sequel is The Invincible Sentinel (and, by proxy, its second form The Invincible Empyrean Sentinel). The Invincible Sentinel is effectively a stronger, upgraded version of the Sentinel fought as the final boss of Borderlands: The Pre-Sequel's story. The Invincible Sentinel is encountered in Eleseer by placing five Moonstones onto each of the four totems (totaling 20 Moonstones) in front of the Vault entrance before walking through it. The normally purple entrance into the Vault will change into a red opening once all totems are paid, signalling that The Invincible Sentinel will greet players inside. In order to summon the Invincible Sentinel, the quest The Bestest Story Ever Told must be either accepted or already completed.