1 - There are two builds (well technically 3, but if you’re starting now… don’t go for the crit build… it requires a lot of investment and you likely won’t make it before corruption is gone) for fire. One is the lucid memory build and the other is the “minute mage” build. Lucid memory uses… you guessed it… lucid memory as it’s major. Even rank 1 lucid is typically worth it, so if you’re going with this then definitely use lucid as your major. If you’re going for the minute mage build, then use worldvein as your major, put visions of perfection in a minor slot, and then take kindling instead of meteor for your final talent. The way to think about these builds:
Lucid Memory build - Think of it like this… you get an enormous combustion every 2 minutes, then do relatively poor DPS while you wait for combustion again. This is the build most raiders use (though this is VERY dependent on add spawn times).
Minute Mage build - This spreads out your damage more as you get more combustions out (ideally 1 per minute hence ‘minute mage’) via kindling + visions of perfection. So you’ll have a strong combust (worldvein+trinket+mechagon bracers) on pull, then a weak combust at the 1 minute mark (worldvein alone), then a strong combust, then a weak, and so on. This is the preferred build for dungeons as you’ll have combust up for almost every pull.
2 - As Benazir said, the point of combustion is to get as many pyro’s out as possible. Because of this, you’ll want to go pyro -> fire blast -> pyro -> fire blast -> pyro etc etc etc. Once you’re out of fire blast charges, swap to scorch between the pyro’s. Why scorch? It’s a shorter cast time and has pretty much zero travel time to the target. Remember, your goal is to get more pyro’s out. Fireball is weak compared to pyroblast.
This is where the Mechagon bracers come in as super strong for fire. The way the bracers work is they reduce the cooldown of the last 3 spells you cast. So you use them once you’ve hit your last charge of fireblast, and won’t get another charge back after you’ve fired off the pyro. Use them BEFORE you cast the pyro. This way your last 3 spells will be: Fireblast, Pyro, Fireblast. Netting you a double recharge on the fireblast. If you do fire off the pyro before using them, your last 3 spells will be: Pyro, Fireblast, Pyro… only getting you 1 recharge from the bracers.
3 - All this tells me is that you’re not running hard enough content. In super low keys, any huge burst AoE spec is going to dominate (DH’s, BM hunters, Outlaw rogues, etc…). Everything’s dead before any ramp class has a chance to do anything. Once you fight stuff with more HP, that’s when you’ll start to see how powerful combustion can be. As for set up, that comes with knowledge and experience of the dungeon. One big recommendation is when you start your combustion, hit the mob with the most HP. If the mob dies before you finish your combustion, then it won’t have a chance to spread the huge ignite to everything else.
Finally, as lots of people ask about how to correctly combust, this is the cast order:
Lucid Memory:
Lucid > Fireblast > Rune of Power > Meteor > Combust/On use trinket > Fireblast > Pyro > Fireblast > Pyro > Fireblast > Pyro > Fireblast (once out, use mechagon bracers) > Pyro > Fireblast > Pyro > Fireblast > Pyro etc etc etc.
You use meteor BEFORE combustion. Meteor calculates its damage 1 second before landing, not when you cast it. As such by using combust after the meteor nets you an additional global for the combustion window that would’ve been wasted casting meteor.
Minute Mage:
Worldvein > Fireblast > Rune of Power > Scorch > Cast combustion before the scorch cast ends ensuring it crits > pyro > fire blast > pyro > fireblast > continue as above using mecha bracers as described above.
Additional note: Becareful with your combust/trinket macro here… combust can cast during the scorch cast, but your trinket won’t go off. Make sure you spam the button as the scorch finishes to ensure the trinket also goes off.
For both builds in raids, you’ll want to pre-cast a pyroblast starting at 4-5 seconds left on the pull timer as well. This will slightly alter the opener depending upon whether that pre-cast spell crits or not. If it doesnt, do what I stated above. If it does, then you don’t need to waste a fireblast charge at the start during the opener.
What to do between combustions? Do your ST rotation on the highest HP mob, and throw out living bombs whenever there are 3 or more targets that’ll live to get hit by the second explosion.
Hope this helps, lemme know if you have further questions.