This guide provides strategies for defeating the Great Unclean One (GUO) on the Exterminatus difficulty. The encounter with the GUO differs on various difficulties. In close range, the GUO’s Doomsday Bell attack is triggered on some difficulties, dealing light damage in an area-of-effect (AoE). However, this attack does not occur on Exterminatus. Another significant change is the Bilesword attack, which is the highest priority. It involves two shockwaves per swing, repeated three times, with each shockwave dealing substantial damage. This attack becomes more challenging when combined with the increasing numbers of Nurglings or when the player gets caught running loops.
Strategies
The strategies outlined here are more aggressive, focusing on facing and defeating the GUO without retreating. However, for players who lack Vortex grenades or heavy weapons, there is a trick that allows for killing the GUO with minimal damage. It’s important to note that the weapons and movements described are examples, and there are various variations that can be employed.
Great Unclean One Attack List
Bilesword
When engaged in an open area, the GUO initiates the Bilesword attack. It slashes with its sword, sending two shockwaves towards the player. These shockwaves move slowly and close enough together, making it relatively easy to jump over both with a single jump. The attack is repeated twice more with a cooldown before the GUO cycles through its other attacks.
Several important details should be considered regarding this attack as it significantly impacts the fight. Firstly, the attack starts only when the GUO has a direct line of sight on the player, and it will skip this attack if line of sight is broken. However, breaking line of sight does not necessarily cancel the attack, as the shockwaves can pass through obstacles like pillars. Due to this, it is advisable to allow the attack to occur and focus on damaging the GUO while jumping to avoid getting hit. Players can utilize weapons with splash damage to kill the emerging Nurglings while playing peekaboo with the GUO. It’s also worth noting that engaging the GUO while it is on an incline can alter the shockwave’s trajectory, potentially removing the option to jump over them. Lastly, the high damage of this attack can trigger the Know No Fear ability, leaving the player with over 100 health. Know No Fear cancels the damage from a fatal blow and grants brief invulnerability, which can be replenished by scoring kills. The plentiful spawning of Nurglings provides an opportunity to retreat, recharge the ability, and re-engage. Purposefully triggering Know No Fear is possible, but using the last barrage of the Bilesword attack is recommended since the attack duration exceeds the invulnerability window.
Nurglings!
If the GUO completes the Bilesword attack, it proceeds to release a swarm of Nurglings from its gaping maw. Utilizing a weapon with splash damage or throwing a grenade at the beginning of this attack effectively eliminates them. Weapons like plasma and melta gun work well, with the melta gun being ideal due to its high DPS and availability of the Munitions Boon in this level. The primary focus should be damaging the GUO itself while using splash damage to deal with the Nurglings, instead of solely targeting the adds and causing incidental damage to the boss. This attack also presents an opportunity to initiate melee attacks on the GUO if its health is critical. It’s important to note that even if the GUO is killed, some Nurglings may still be present, and weapons like the volkite blaster can be used to clean them up effectively.
Puke Bile
During this attack, the GUO plants its sword in the ground, opens its mouth, and releases a prolonged poison stream similar to that of plague toads. The attack weakly tracks the player and is not particularly dangerous if the player keeps moving, providing an opportunity to continue damaging the boss.
Doom Bell
On the Exterminatus difficulty, the GUO does not perform the Doom Bell attack. This attack has a relatively high priority and is triggered when the player is in close range. It involves the GUO channeling and dealing modest AoE damage. On lower difficulties, players may bait this attack and deal damage from a distance or endure the damage if using melee.
Kill Methods
Method A: Vortex Burndown
With even just a pistol start, it is possible to kill the GUO within 10 seconds and sustain no damage. There is a Vortex Grenade available just before the boss, along with a melta gun, a machine spirit, and munition blessing found elsewhere in the level. Throwing the Vortex Grenade at the beginning allows the player to jump over a single Bilesword attack, and the fight will conclude before running out of melta gun ammo. While the plasma weapon is also viable with the machine spirit, the risk of splash damage is unnecessary.
Method B: No Retreat
Move to one side and use the plasma to damage the GUO during the first Bilesword attack. Throw a grenade and continue attacking during the Nurgling spawn. Timing a reload just before tossing the grenade is helpful but not essential. When the GUO starts using Puke Bile, approach it and circle around while unloading the melta gun. The goal is to position oneself to deal with the subsequent attack, which may involve jumping over another cycle of Bilesword slashes.
At this point, there is a good chance that the GUO’s health is low. In such cases, breaking line of sight can lure out another round of Nurglings. Toss another grenade and resume firing, finishing with melee attacks when the GUO’s health is critical.
Method C: Grind the Gears
Shoot the GUO with any weapon while evading the first Bilesword attack. After the attack, run down and to the right of the boss, where a set of deadly gears is located. Sprint and jump over the gears, landing on the narrow ledge on the other side, and wait.
The Nurglings will be killed by the gears, and the GUO will eventually make its way toward the player. Unload any weapon, even a standard boltgun. While it is necessary to jump over the Bilesword attacks, it is relatively easy at that distance and poses the only risk to watch out for. Occasionally, there may be a need to sidestep some poison attacks, but they occur infrequently, and the damage is minimal. The fight will be concluded in less than a minute.
