Lord Jaraxxus is the second boss in TotC, one of the demon lords he’s a bit of a pain but on balance a simpler fight than the beasts.
The keys to the fight are target switching (adds must be nuked down quickly), situational awareness to get out of the bad and targetted healing. Ranged (inc healers) need to spread around the boss, Fel lightning can chain to keep a reasonable distance between each other, the fireball should be interrupted (DKs I’m looking at you).
Every 60 seconds, Jaraxxus alternately spawns a Nether Portal or a Fel Volcano. Nether Portals spawn a Mistress of Pain, while Volcanoes spawn 3 Felflame Infernals. Both types of adds must be tanked and nuked down by ranged as fast as possible. Melee should stay on the boss. So ranged, save your damage cooldowns for the adds.
Jaraxxus will randomly cast Incinerate Flesh on one raid member. This debuff absorbs all healing on that target until a certain amount of healing has been done, if the debuff wears off, the target blows up, causing a Burning Inferno to hit the entire raid for large amounts of damage over time, this can be a wipe (it’s a insta-wipe for heroic mode).
Legion Flames is the other nasty, if a member gets this cast on them they should run outside of the raid and then run around. As the debuff ticks down it will drop green flame on the ground, so while running a line of green fire is left behind the target. Therefore it is essential to be careful with the path to avoid running through the healers or ranged dps. The Nether Power debuff will need dispelling by the priest to reduce his dps.
So, hit the boss, hit the adds, get out of green, heal the bad debuff, dispell the other debuff, win, loot, /cheer.
Then… faction champions…
[Edit: Legion flames updated]