Start with Fireproof Mantle equipped its absolutely needed here and grab Body-Cooling Powder before heading in. Cloud Step and heavy attacks are your main tools here gonna need them for dodging and damage. First phase keep close to him, use Cloud Step when he tries creating distance with his spear attacks and fire moves just watch the timing. Around half health he jumps up making copies of himself, back away from center and use rocks as cover while staying locked on the real one.

Duplicates will rush you with spears so dodge any direction that's clear, Cloud Step helps spread their attention. Final phase gets nasty with longer spear spins and fire patches on ground, stick close but dont get greedy even with fire defense youll take damage. Trick is staying aggressive while keeping enough stamina for defense, like a dangerous dance really. Maybe interesting that upgraded fire resistance makes huge difference here so check your gear first. Keep pushing damage when safe but always ready to dodge those flame attacks, and remember healing items work best behind cover when he's doing his duplicate move.