Stand in the middle of the circle and drop your bat bone
Head inside the door. Go up 2 stories and kill Sir Mordred, who is level 39. Morgan Le Faye will then appear. Ask her to help save Merlin. You’ll be requested to obtain 4 DFO Gold items, one of which is some magic words.
Head out of the keep on the west side and kill a bat. Collect its bone. Get yourself a loaf of bread. Then talk to Lady of the Lake southeast of Taverly. Ask to have Excalibur.
Make your way towards the Jewelry shop in Port Sarim. Open the front door and a beggar will appear. Give the beggar your bread and she’ll turn into Lady of the Lake, which will then hand you Excalibur.
Head to the prayer altar in southeast Varrock. Check it to find 3 magic words. Now that you have the bat bone, lit black candle, Excalibur, and acquired the magic words, head underneath the shelter northeast of Camelot Castle. Stand in the middle of the circle and drop your bat bone.
A Spirit will then appear. Chant out the magical words “Snarthon Candtrick Termanto” and then wish to free Merlin from the crystal. The Spirit will obey your command.