How to Find Sorceress Sellen and Complete Her Quest

First Meeting - Waypoint Ruins Cellar: Find Sorceress Sellen in the cellar beneath the Waypoint Ruins. Access the cellar by jumping the wall south of the Giant Flower and descending the stairs. You will encounter the Mad Pumpkin Head boss. Defeat him to access Sellen's room. Speak with her; if you wish to study Sorcery, reply affirmatively. She will sell various Sorceries, including Glintstone Star and Scholar’s Armament, and you will receive the Nod in Thought gesture. Spells available include Carian Slicer (1500 Runes, requires Royal House Scroll), Crystal Barrage (1500 Runes), Glintstone Arc (1500 Runes), Glintstone Pebble (1500 Runes), Glintblade Phalanx (2500 Runes, requires Royal House Scroll), Glintstone Stars (3000 Runes), Scholar’s Armament (3000 Runes), and Scholar’s Shield (2500 Runes).

Second Meeting - After Meeting Azur: Travel to Mt. Gelmir and explore the Hermit Village southeast of Volcano Manor. Find the Sorcerer Azur near the Hermit Village Site of Grace. Interact with Azur to obtain the Comet Azur Sorcery and trigger the next step. Return to Sellen at Waypoint Ruins. She will ask you to find Master Lusat and give you the Sellen Sealbreaker. Travel to Caelid, head northeast from the Church of Plague to a graveyard. Find a large tombstone, then run to the cliff behind it and strike it to reveal a hidden passage to the Sellia Hideaway dungeon. Progress through the dungeon, drop down the second large pit to the bottom, and find the locked door. Break the seal to speak with Lusat and obtain the Stars of Ruin Sorcery.

Third Meeting - After defeating Starscourge Radahn: After defeating Starscourge Radahn and meeting Witch-Hunter Jerren in the castle plaza, return to Sellen at Waypoint Ruins. She will ask you to meet her at the Witchbane Ruins in the Weeping Peninsula, Limgrave. Travel to the west of the peninsula to find these ruins. Descend the stairs to find Sellen's imprisoned body. Speak with her and agree to help to obtain Sellen’s Primal Glintstone.

Fourth Meeting - Three Sisters, Liurnia: Travel through Liurnia of the Lakes to Caria Manor. After defeating Royal Knight Loretta, exit the manor north to reach Three Sisters. Locate the ruins between Ranni’s Rise and Renna’s Rise and kill the singular Sorcerer there. Strike the ground to find hidden stairs leading to a laboratory. Go to the back of the room and slash the wall to find another hidden passage revealing Sellen. Interact with Sellen to place the Primal Glintstone, transferring her soul into a new puppet body. Return to the Witchbane Ruins; Witch-Hunter Jerren will remark that Sellen has escaped.

Final Meeting - Raya Lucaria Academy: After clearing Raya Lucaria Academy, return to the Raya Lucaria Grand Library Site of Grace. Outside the door, you will find two summon signs. A gold sign summons you to aid Sellen against Witch-Hunter Jerren, resulting in Jerren’s death and ending his questline. A red sign allows you to invade Sellen and assist Jerren, ending Sellen’s questline. You must choose one path. If you aid Sellen, you will obtain the Eccentric’s Armor set after defeating Jerren. Return to the Grand Library and speak with Sellen to exhaust her dialogue; she will give you the Glintstone Kris and offer the Shard Spiral spell. If you have already visited Lusat, refresh the area and speak to Sellen again, then repeat. Rennala will return, and Sellen’s appearance will change. Speak with her again to obtain the Witch’s Glintstone Crown. This concludes Sellen’s Questline.