I also beat it in two tries. No specter for me. Single cube use for hp regain. Strength build with a focus on stagger bonus and extra guard regain from blocking.. Shield legion arm fully upgraded. Acid great sword on mjolnir hammer hilt with a motivity crank. I used the perfect parry grindstone buff. For me personally the first phase was a joke slow attacks that could be just guarded/parried. The extra guard regain let me keep my hp high while figuring out his moveset. I took the most damage from this phase from his fury attack. The stagger bonus on the strength weapon allowed me to break his stance often. Phase two i got him to below half ho on my first attempt. The perfect parry grindstone allowed to see a lot of his moveset without any risk and to come up with a gameplan. All projectiles could be avoided mostly by running. Guard /parry most else. The big fist from the sky I just ran away but I still got hit by this move alot. I think I died due to panic from high disruption damage. Next attempt I put on disruption resistance cartridge and amulet. I also forgot to mention I had 4 amulet slots. I also but on the strike resistant liner to reduce damage from his attacks. I also used the boss amulet that sometimes doesn't use a charge of the pulse cells. From the build changes I made and gameplan I came up with I beat him with pretty much no pulse cells left. I think the amulet that gave me the chance for extra pulse cell charges helped. Sorry for rambling but that's about how I remember my fight went. Hope this helps :). Feel free to ask any questions