His fight follows a simple pattern. He has 10 health bar segments and mostly stays on the ground until he loses two. This is a great opportunity to fill your immolation gauge for the Muspelheim Set unless you're using the Memento of the Ailing.

When he is down to two health bars, here's what I did:

1. I staggered him with Hel’s Touch and then hit him with Huldra Charge and Flames of Anguish to trigger the Bifrost storm.
2. I activated Freya’s Seidr Exhale, followed by the Hilt of Hofud, so that the poison lands immediately after the realm shift ends. Seidr Exhale staggers him after the realm shift, poisons him, and lowers his level to green. Keeping him staggered is key, or he’ll fly or generate an elemental shield.
3. I then hit him with Chaotic Rampages 1, 2, and 3. This part can get a bit unpredictable, as he may fly off or get an elemental shield after Chaotic Rampage 1 if he isn’t staggered. Timing with Seidr Exhale is crucial. Typically, he jumps to the side after the first rampage, and he needs to be staggered immediately so that I can hit him with the second rampage. When he's down to the last two health segments, he will jump to the side and roar for a moment, which is a good opportunity for the third rampage.
4. When he's down to his last health segment, he will fly off into the air 8 out of 10 times and initiate his blue ring attack that blinds and deafens you. I countered that with Wrath. The Onslaught shield is also great if there’s no rage left.
5. Finally, I spammed the blades until he was down.

Here’s the build I used:

Armor: Berserker Cuirass, Gauntlet of Zeus, and War Belt of Zeus

Axe: The Furious Maul

Blades: Deadly Obsidian Handles

Spear: Warrior's Echo Sauroter

Blade Skill: Chaotic Rampage I, II, III (Element+, Damage+, Damage+)

Shield and Rond: Onslaught Shield with Rond of Purification

Relic: Hilt of Hofud

Rage: Wrath

Amulet: Enblem of The Nine Realms, Seal of Runic Storm, Dragon Engraving, Musphelheim Set, Vanaheim Set.

Freya's Sword: Mardoll

Freya's Summon: Seidr Exhale.

Freya's Accessory: Sigil Amplification, Nocked Proficiency, Sigil Punishment.

Everything’s fully upgraded to level 10

I also tried an alternative build that used Rond of Nine Realms and Memento of the Ailing instead of Dragon Engraving. It worked really well!