Velka's Pact Quest

You can do the rest of the game in any order before, during, or after the following steps, as long as you do the steps strictly in order, i.e you must save the sinners until after making the pact for it to count. Also note the questline requires doing alt path DLC, so don't forget to do that before Anor Londo to avoid locking yourself out of it. It is recommended to do the Ashen Ring quest before or alongside this one, as it helps with the fight at the end.
 * Enter the Painted World, and just after the bridge you spawn on, explore to the right in the cliffy area for a raven.
 * The raven takes you back to Firelink and prompts you to make a pact with Velka. Accept.
 * The following events break the pact: Killing the Gravedaughter, killing Priscilla, and Killing The Fair Lady and the new Izalith NPC. NOTE: due to a bug in Jeremiah's quest, letting Quelaag's sister die after Jeremiah steals your cthonic spark will also count as a sin, breaking the pact.
 * Kill Sinners to appease Velka: (any order)
 * Complete Ciaran's quest, then punish Gravelord Nito for his sins by killing him.
 * Complete Havel's quest and get his drops to punish Seath for his sins.
 * Punish Jeremiah for his sins by killing him when he attacks.
 * It may be possible to prevent breaking the pact if he kills you after you rescued the DoA NPC.
 * Punish Gwyn for his sins by killing him.
 * After killing Gwyn, walk out of the kiln and back up the stairs, where the Velka raven is waiting. If you've done everything correctly, there is a prompt to travel to the past to fight Gwyn, Lord of Sunlight.
 * If you did the Ashen Ring quest, wear Gwynevere's ring to gain assistance from black knight phantoms during the fight.