Across the swamp to Chaos Witch Quelaag, the second Bell of Awakening and the Chaos Servants.
Quelaag's lair is the web-covered mound at the far end of the Blighttown swamp. Past her lies the second Bell of Awakening, which opens the gate of Sen's Fortress, and below the bell a hidden room with a bonfire and the leader of the Chaos Servants. Both the boss and the bell change things elsewhere, so read the two warnings before you act. Bring your best fire protection: Quelaag fights with fire and lava.
Help for the fight
If you beat Maneater Mildred's invasion in the swamp while human, her summon sign waits in front of the fog, and she draws Quelaag's attention while you work on the sides. Armor and a shield that resist fire help a lot, and so does a buff such as Flash Sweat.
Before you kill Quelaag
Her death closes, for this run: Maneater Mildred's invasion in the Blighttown swamp, with her Butcher Knife and the Humanity she drops. Mildred comes only while you are human and Quelaag lives, so beat her first if you still want them.
Chaos Witch QuelaagBoss
Location
Quelaag's Domain · Quelaag's lair – Leave the Blighttown Swamp bonfire's tunnel and turn right, keeping the swamp wall on your right: past the wooden ramp lit by torches, make for the odd mound at the far end with a cave halfway up it. Infested Barbarians on the left throw boulders you can't block, so hug the right side (a Cragspider or two and the mosquitoes still need watching) and run into the cave. In the tunnel, leave the Egg Carriers alone: they don't fight, and killing one lets out maggots. The fog waits at the end. In the fight, keep to her sides and back; roll sideways out of her sword thrusts instead of blocking. When she strokes the spider's head, lava spit is coming, so get behind her; when she crouches and the spider curls up, back off before the blast. Run too far and she leaps at you spitting lava, so stay fairly close.
With both bells rung, the world moves on. Siegmeyer leaves his seat by the Sen's Fortress gate beside the Undead Parish bonfire: if you haven't heard him out there (talk until his lines repeat), his later steps can stall. Lautrec leaves Firelink Shrine, so collect his Sunlight Medal there first if you freed him, and the Firelink bonfire can go out of use for a long while. Domhnall moves from the Depths up to Firelink, shop and all (he may stay put until the Sen's Fortress boss is dead). Kingseeker Frampt wakes at Firelink, and the gate of Sen's Fortress opens.
Ring the second Bell of AwakeningQuest step
Location
Quelaag's Domain · Bell tower – From Quelaag's arena, carry on the way you were going and climb the stairs she came down. Follow the hall at the top into a round room with a hole in its floor: the lever is on the far side from the entrance, with a doorway on your right. Pull the lever to ring the bell.
Quelaag's Domain · Bell tower – Plays by itself once the second bell rings, as long as the first bell in the Undead Parish is rung too. The gate is on the bridge reached through the doorway beside the Undead Parish bonfire.
EingyiHidden spoiler – activate to revealNPCMinor spoiler
Location
Quelaag's Domain · Lower bell-tower floor – From the bell lever, take the doorway on the right and go down the stairs (or drop through the hole in the floor). At the bottom, a broken gap in the wall on your left leads off toward the Demon Ruins; instead cross the room past the round platform and strike the wall on the far side, which is an illusion (an orange soapstone shows it). Eingyi blocks the passage behind it: when he asks whether you are a new servant, answer Yes and he steps aside. If you said No, reload and ask again.
Bonfire: Daughter of ChaosAreaMissablePoint of no return
Location
Quelaag's Domain · Daughter of Chaos room – From the bell lever, take the doorway on the right and go down the stairs. Cross the room past the round platform (not the broken gap on the left) and hit the wall opposite: it is an illusion. Answer Yes to Eingyi, the egg-headed man behind it, so he lets you through, then light the bonfire beyond.
Why you can lose it
Light it and rest here before anything happens to the Fair Lady beside it. Never attack the Fair Lady: if she dies, her bonfire goes out and the Chaos Servant covenant is closed for the rest of this run.
Point of no return
Beating Gwyn, Lord of Cinder, then lighting the bonfire or walking out of his arena: either ends this run at once and starts the next one.
Quelaag's Sister (Fair Lady)Hidden spoiler – activate to revealNPCMinor spoiler
Location
Quelaag's Domain · Daughter of Chaos room – Beside the Daughter of Chaos bonfire, half sunk into the wall on the right. You hear her words only while wearing the Old Witch's Ring; without it you can still join her covenant.
Covenant: Chaos ServantHidden spoiler – activate to revealQuest stepMissablePoint of no returnMinor spoiler
Location
Quelaag's Domain · Daughter of Chaos room – At the Daughter of Chaos bonfire, talk to the Fair Lady beside it and accept her covenant. Joining moves you out of your current covenant (you can switch back at a bonfire later), and leaving a covenant can cost half of what you have offered to it.
Why you can lose it
Join while the Fair Lady lives. Never attack the Fair Lady: if she dies, her bonfire goes out and the Chaos Servant covenant is closed for the rest of this run.
Point of no return
Beating Gwyn, Lord of Cinder, then lighting the bonfire or walking out of his arena: either ends this run at once and starts the next one.
Great Chaos FireballHidden spoiler – activate to revealSpellMissablePoint of no returnMinor spoiler
Location
Quelaag's Domain · Daughter of Chaos room – The Fair Lady hands it over as you join, at the Daughter of Chaos bonfire.
Why you can lose it
Join the covenant while the Fair Lady lives. Never attack the Fair Lady: if she dies, her bonfire goes out and the Chaos Servant covenant is closed for the rest of this run.
Point of no return
Beating Gwyn, Lord of Cinder, then lighting the bonfire or walking out of his arena: either ends this run at once and starts the next one.
Shop: Servant RosterHidden spoiler – activate to revealKey itemMinor spoiler
Location
Quelaag's Domain · Daughter of Chaos room – Buy it from Eingyi, beside the Daughter of Chaos bonfire. It is on sale from your first talk with him; his other wares wait until you come back with an egg-infested head.
Rank +2 with the Fair Lady takes 30 Humanity offered in all and pays out Chaos Storm, another pyromancy for the trophy; Eingyi's Toxic Mist needs you infected by an egg. The route does both in the Demon Ruins section, so there is no need to offer Humanity yet. Never attack Eingyi or the Fair Lady. And if Laurentius at Firelink now asks where you found your new pyromancy, answer No.
To leave, go back up to the bell room and out through Quelaag's arena and the Egg Carriers' tunnel to the swamp. The broken gap on the lower floor leads down toward the Demon Ruins, which the route takes much later.