He will automatically discard some chewed bones. Burn them out on OSRS gold a pyre ship. When nothing happens, talk to Otto Godblessed relating to it. He'll indicate a potion to assist. Make a rest potion out of soul weed and snape grass. Use it on your pyre boat, light it, and also a spirit will appear and provide you a key. He will state you must also wield elemental ability and command both body and mind. Proceed to the elemental workshop to the area that has the zapper seat and across from it is a locked door with all the entire body rune symbol on itOpen it with your key and hunt some shelves for the book of the elemental spear.
Go upstairs and make an elemental spear with 2 clad mind bars. Return to the body room, wield your new spear, and pull the lever in the middle. You may sew only thoughts armor against the Homunculus. When the battle is finished, your mind armor will have turned to Elemental Balance Armor. This armor has gentle melee stats. The spear (or, if you have improved sufficient through barbarian training, hasta) has moderate melee stats, and will auto cast spells too.
Go Back to the Ancient Cavern and try to go through the Mithril Door. You may triumph. There'll be several Nightmare Terrors and Nightmare Spikes (Nightmare Spike-level 62, ranged user, can switch off your prayer randomly) attacking you. At the center, the critters will vanish, and buy RuneScape Mobile gold also a phantasm appears. He clarifies that the Nightmare Creatures are pawns of whomsoever summons them, so the two Zamorakians and Zarosians can utilize them. The Phantasm has been revealed to be a part of Zaros's soul. He'll attack you, inflicting huge harm if you don't have a minumum of one bit of elemental balance armor, or the weapon.