Your path to the final Lord Soul is filled with some of the toughest challenges the game has to offer. From Quelaag's Domain, head down the path to the entrance of the Ruins. If you haven't beaten the Ceaseless Discharge yet, head down the hill and around the lava lake to face the foe.
EditBoss Fight: Ceaseless Discharge
As you can see from our video below, there's an easy way to defeat the giant beast without having to swing your sword at all. If you do intend on fighting it fairly, your best bet is to head to the large open area near where you originally grabbed the items. If you stick close to the monster, he will use only melee attacks instead of his incredibly powerful slam move. Watch for his tell as he raises his arm and roll out of the way just before his arm hits the ground. This will give you a few moments to spam it with powerful spells and attacks. Repeat this to take down the Discharge and cool the lava at the bottom of the Ruins.
With the Ceaseless Discharge dead, head back down to base of the area. This area is adorned with a herd of Taurus Demons, the boss you fought originally on the bridge in the Undead Burg. Lure them to you one at a time to avoid being outnumbered. There are some great items at the back of this area, but they are surrounded by deadly lava. Make a note of their placement for a little later on once you've acquired the Orange Charred Ring.
Head down the stone path along the side of the cliff, battling past the Minor Capra Demons. Use the bonfire at the bottom of the stairs, then head back to the fork in the path. To the left is a thin walkway guarded by enemies. If you can make it to the end, your prize is a Large Flame Ember. Regardless of your decision, your ultimate goal is up the stairs through the fog gate. Here you'll have to face off against a Firesage Demon, an upgraded version of the Asylum Demon that you fought at the very beginning of the game. Use the same tactics as before to make quick work of the beast.
After the fight, you'll find yourself at a set of stairs that go up and down. Head up to find an elevator that leads back up to Quelaag's Domain. Once the shortcut is opened up, head back down the elevator and descend the staircase. Rest at the bonfire and continue down the root until you find yourself standing before yet another fog gate. The final beast of the Ruins sits on the other side, so prepare yourself for a fight before you cross the threshold.
EditBoss Fight: Centipede Demon
Compared to the other enemies in the area, this boss is a bit of a pushover. A majority of the chamber is filled with lava, so just stick to the safety of the platform at the beginning of the room. The Centipede's main attacks come in the form of an array of punches that have a fairly obvious tell. Roll to the side to avoid his swipe, then hack away a few times. A high intelligence combined with a few direct hits from your Soul Spear will make quick work of the Demon. For the magically inept, just concentrate on avoiding the Centipede's long arms and deliver a few blows before going back into defensive mode.
Once you've bested the beast, you'll be rewarded with the Orange Charred Ring. Equipping this will allow you to walk on lava and receive only minimal damage. For you perfectionists, head back to the opening area of the Demon Ruins and grab the items that was surrounded by lava. For those of you who are impatient, head to the left side of the chamber and go through the cave to finish up the area.