The Bed of Chaos

 is a boss in Dark Souls, found in Lost Izalith. It is possible to reach this boss without fighting Demon Firesage or the Centipede Demon. This is done by offering Quelaag's Sister 30 Humanity through the Chaos Servant Covenant.

Lore
The Bed of Chaos was once the Witch of Izalith and some of her Daughters of Chaos. They were all mutated by the Witch's failed attempt to recreate the first flame.

Strategy

 * A common strategy is to summon one or two phantoms and position both next to each Orb, with the Host out of reach of the Bed of Chaos's arm sweeps but in a direct line towards the entrance to the 'bug' itself. Both phantoms break the Orbs one after the other, allowing the Host to jump to the entrance of the Bed of Chaos's 'mouth' and kill the boss.
 * A simple strategy basically involves 'corpse-running' to the fog door, and then running desperately to each Or and then to the Bed of Chaos itself. Some players prefer to stay hollowed so that humanity is not wasted, since many deaths will likely follow after the first Orb breaks.

Double Swipe
The enemy will use this attack as you near the middle of the area. The Bed of Chaos will swipe its left hand across the floor and then do the same with its right hand. This attack can be blocked, but that does consume a large amount of Stamina making it more difficult to block the second attack.

Slam
The enemy will raise its hand up into the air and then slam it onto the ground. You can avoid this attack by running away from the arm before it hits the floor.

Fire Pick
After destroying one root, the enemy will gain an arm made of fire. The enemy attacks by hitting the floor, and then digging in a straight line towards the back of the area. You can avoid this attack by running or rolling to the side as it only travels in a straight line. It can be blocked, but you will need a shield with high resistance to fire.

Double Fire Pick
After destroying the second root, the enemy will gain a second arm made of fire. This attack will use both arms to hurt you, but can still be avoided in the same way.

Burning Explosion
The enemy will use this attack after both roots are destroyed. It will begin to make flames appear in the area to which it then erupts, causing huge fire damage. When the surroundings begin to flame up, you will need to find areas where the flames do not appear, as these are the safe spots from the attack. Some safe spots will appear at the edge of the arena.