He uses Ancient Magics, including Miasmic, as well as ranged along with a melee attack using a power whip. Defeating him is more of a struggle of wits than most battles you fight. He seems in the middle of the point, does an emote, disappears, launches an attack (at the ground, not in you, so that you are able to dodge), disappears, rinse and repeat. I won't go into specifics about what occurs, come up with it yourself. If you understand what attack is coming, but not where it is going to be you can use astrology, but everytime you use prayer to block an attack, your prayer is drained a few points.
Also, the only potions which have impact in here are the barbarian"mix" potions. When the Phantasm is dead, he will laugh and say your attempts are pathetic in the surface of Evil Incarnate. However, you did make him vanish for a little while. Head to the north of the area and there will be a dark crystal .I am not extremely satisfied with the way this came out, and I am also well aware that the name for your armor is idiotic. I am still trying to think of a better title for this. Let me know if you have some suggestions to improve the quest.
Royal Experiment. Start: Talk to King Vargas within his castle in Miscellania. Skills: 30 Crafting, 40 Smithing, 20 Structure, 30 Slayer, 40 Mining, 50 Agility and 60 Defence. You should also have completed the Pirate Pete part of Recipe for Disaster.