Heroic Warmaster Blackhorn

[:1]Anybody able to give tips that has killed this as a fire mage? Looking for any tips.

With the large amount of movement needed, it's difficult to build stacks of the two set. Combustions have been kind of week and/or drakes die before you can get one off or spread it.

I seriously don't want to have to go arcane but I'm already expecting to be arcane for Heroic Spine.

The group make-up we use includes a shadow priest. So, the two of us are soaking with CDs.
You should only be moving to soak the big hits and single-soaking any nearby small ones - and then only soaking the small ones when Cauterize is available. As long as every big hit is fully soaked and all sappers are killed, you should only need to block a handful of small ones throughout the entire fight. For the small ones, I will only go for them if I have to refresh LB or a Hot Streak proc, so there is no loss in damage over standing still, and will only move to within a few yards of my position.

Your tanks should be positioning humanoids to one side of the ship, in range of cleaves with that drake. That gives us three targets to spread dots to, so Pyromaniac is great here. Also, when new drakes fly overhead to drop fresh adds you can target and LB one of them to get Pyromaniac up again. When going for a strong Combustion, you can create it on any of the targets as the opportunity presents itself, and cleave it from there. It can be better to create it on the dreadblade instead of the drake since the dreadblade has more health (and combustion will run to full course), and you can cleave it onto the drake and the slayer too anyways. Also, generally speaking I think the dreadblade is more deadly to the raid so it should be getting focused first anyways.

Impact is a good stun for sappers, if your raid is short on death grips or other stuns.

There are other things that can be done at the raid level too. Make sure that drakes are killed before they fly off. They cast more barrages when they fly away - which means you have to soak more. The only exception is you might want to purposefully allow one to fly away at low health to ease the transition into phase 2 (gives you more time to finish off the humanoids so they aren't charging people during the start of p2). Another thing that we find helps a lot is to have the entire raid except for mages/shadowpriests stack together and just heal through the charges. Occasional barrages will hit the group, and that's just fine. This helps keep the rest of the deck clear so the soakers can see the charge lines and avoid them, which helps a lot with inadvertent Cauterize procs. It also means we have to move a lot less to avoid charges heading to other people.