Hah, figures, when I try again today, I get him on the second try.
Guess I'll list some tips myself then.
First phase of the first is real easy. The Whirling Hammer move is the go to move for the whole fight really. If he gets two close, use the LT RT hammer move to stun him, then just keep hitting him with the Whirling Hammer until you can grapple him, you need to destroy both of the purple gems on his armor, one on the back, one on the front.
After you do that with the Y power attack on both sides, he'll run off and summon some normal enemies. Use grapple moves on the smaller ones to get back health and Odinforce, whichever you need. Once he summons three of the bigger fire demons. Use a storm on them to get your rage maxed, and use it.
Now his second phase is much harder then his first, since he'll have more moves. You'll still wanna just keep spamming the Whirling Hammer move.
There are a couple of his attacks you wanna watch out for. When he raises his sword above his head, and brings it back down, he's summoning some fireballs to rain down on you five times, so you'll want to keep moving when he does this. I'd say that was his most damaging attack to me at first, since I hadn't learned to recognize when he did them. The other move is when he shoves his sword in the ground, and summons two fire waves you need to jump over. Just jump over them, don't jump and air dash, since if you do that, you might hit the second wave on your way down.
His other attacks aren't too hard to dodge, as long as you keep a good distance away from him, which is what you want to do anyway, since you'll mainly just be throwing Whirling Hammers at him. I went the whole fight without using any melee attacks at all.
Once he gets lower in heath, he'll try to grapple you, these are easy, since all you have to do is mash X each time, but make sure once you get to his face, you attack right away.
That's about it. Just keep throwing Whirling Hammers at him till your rage is full, and use it.