He'll state you must also wield elemental ability and RuneScape gold command both body and mind. Go to the elemental workshop into the area which has the zapper chair and across from it's a locked door with the body rune symbol on it* Open it with your key and search some shelves for the publication of the elemental spear.
Go upstairs and make an elemental spear using 2 primed mind pubs. Go back to the body room, wield your brand new spear, and pull the lever in the center. You will stand on a giant Body Rune Symbol, along with a level 400 homunculus will appear. While fighting, your stats will be boosted dramatically.
You may sew only thoughts armor against the Homunculus. When the battle is finished, your brain armor will probably have turned to Elemental Balance Armor. This armor has gentle melee stats. The spear (or, even if you have progressed enough through barbarian coaching, hasta) has moderate melee stats, also will auto cast spells as well.
Go Back to the Historical Cavern and try to go through this Mithril Door. You will triumph. There will be several Nightmare Terrors and Nightmare Spikes (Nightmare Spike-level 62, ranged user, can turn off your prayer randomly) attacking you. At the middle, the creatures will vanish, and also a phantasm appears. The Phantasm is revealed to be part of Zaros's soul. He will strike you, inflicting huge damage if you don't have a minumum of one piece of elemental balance armor, or even the weapon.
He utilizes Ancient Magics, including Miasmic, in addition to ranged and a melee attack using an energy dip. Defeating him is more of a battle of wits than many battles you fight. He appears in the center of the point, does an emote, disappears, starts an assault (at the ground, not at you, so you are able to dodge), disappears, rinse and repeat. I will not go into specifics about what occurs, come up with it yourself. If you know what attack is coming, but not where it's going to be you can use astrology, however everytime you use astrology to buy RS gold block an attack, then your prayer is drained several points.