Originally Posted by
DarkSoul
Link your armory so we can look through your gems, reforges, enchants, spec and glyphs.
That being said: Haste to 2005 Rating or 1505 rating if you have 4t13. After that, mastery is better than haste, and crit is always best. If you have less than 1555 haste in 4t13, never cast Combustion with less than 10 stacks of Stolen Time. The exception to this is if you have Insignia of the Corrupted Mind, which lets you cast Combustion regardless of stacks as long as the trinket is active.
Once you're in raid:
Hardcast Pyro on the pull, and only on the pull. This puts up Critical Mass, and CM should always be on the target.
Keep Living Bomb up on your target, but always let it explode. Don't refresh it early.
Keep Flame Orb on cooldown.
Unless you have an addon to track your ignite ticks, wait until after a big pyroblast crit to cast Combustion.
Dot Spreading:
Your Impact talent will cause a proc that finishes the cooldown on your Fire Blast spell and causes it to spread any dots on your target to all targets around it. During combat, the only time you will ever use Fire Blast is when there are adds around to spread dots to. Let's take Black phase of Yor'sahj as an example.
You run out, kill the slime, then get back to the boss and start putting up your dots. Get Living Bomb up, spam your Fireball and fish for a Hot Streak proc with a good sized ignite while the adds are spawning. About the time the adds all get to where you're stacked up, you'll ideally have all three dots on Yor'sahj. When they're all coming in, hit Combustion to get it rolling, then Blast Wave all the adds to force an Impact proc. As soon as it pops up, hit Fire Blast and your Living Bomb will spread to two of the adds (since it's got a three target limit), and Ignite, Pyroblast, and Combustion dots will spread to every add in the pull.
The reason you use Blast Wave is because of Improved Flamestrike and the mechanics of Impact. Impact has a 10% chance to proc whenever a spell deals damage. If you Blast Wave on 8 mobs at once, that's 8 chances for Impact to proc. The free instant Flame Strike also hits those same 8 mobs, each hit also having a chance to proc impact. Usually you'll be able to "force" it to proc when you need it like this.