Phase One: Everyone is positioned 6 yards apart and the tanks engage the boss. The only major tanking mechanic is tank swapping once the tank takes too many stacks of Raggy's debuff. Other than that you just watch out for flame waves from his Sulfrus Smash mechanic. You can do this by either being up in melee or positioning yourself at a diagonal from the impact point.
Throughout the fight he will do a single target knockback and an AOE knockback called Hand of Ragnaros. Just make sure you don't get knocked into a lava wave or a magma trap and I usually cycle my defensive cooldowns for each Hand. We didn't fully understand where it came from but we believe that if your casting within 6 yards of another player (or are in melee) when he casts one of these effects you could be spell locked for a few seconds.
Finally Ragnaros throws down fire traps that will detonate if someone stands on them and launch the unsuspecting shmuck into the air to fall to his death. We had a priest detonate these and then slowfall himself since they will stay active the entire fight if not detonated. Eventually we switched to our Mage who could apparantly safely blink through them and then they would detonate.
First Intermission: In this phase Ragnaros smashes his hammer down in one of three places, which summons 8 fire dudes who speed straight towards his hammer. If they hit it they do massive damage and then wipe the raid. We had big elaborate diagrams to deal with this but they were too confusing so we ended up just assigning DPS to each add spawn depending on the position of the hammer.
The adds move fast but slow down the lower their health is so the best way to deal with this phase is to tab target once the adds are half health and then finish them all off before they get to the hammer. We also used stuns, knockbacks and death grips to buy more time.
Second Phase: This phase is probably the hardest and most chaotic. It seems completely random and hectic but actually it isn't. It's a 100% predictable because all of the mechanics occur in exactly the same order. The only RNG is where the Engulfing Flames will appear but you can anticipate and avoid them easily.
Sulfurus Smash returns as well as 2 other mechanics. Seeds will drop every minute on all raiders and if your quick you can actually dodge the impact. Everyone has to remain 6 yards apart or else you can take splash damage. They then will detonate and do damage depending on how far away you are from the seeds. Finally they spawn a bunch of elemental adds that can't be tanked and get AOEd down. How we handled this for the most part is grouped up 6 yards apart on one side of the platform and when seeds landed ran to the other side. Raid cooldowns were effective here to mitigate the damage from the seeds and the elementals.
The final mechanic is engulfing flames, which is a simple fire wall that takes up one of three areas of the platform. Stay out of this. Our biggest challenge was after grouping up for the seed detonation either a flame wall or a smash will appear and kill a few players. We realized this was the predictable part and I'll explain the chain of events.
Phase, Group up 6 yards apart east side. Smash. Seeds. group up west, 6 yards apart. Flame wall. Kill adds. Avoid smash by standing in melee. spread out, avoid wall. Seeds. Group up east in melee to avoid smash. wall. Spread 6 yards avoid smash. Seeds. Run west. Wall. Kill adds. Phase. If this makes sense to you, phase 2 is easy.
Second Intermission: Same as the first except a little tougher since two large adds spawn that have to be tanked. DPS ignored them and killed flame dudes. The large Scion adds put a debuff on you like engulfing shadows which leaves a flame trail in your steps and heals the little guys so you just kite away. We left one little add up but slowed to prolong this phase and killed one scion and brought the second down to like 30% to be finished off in phase 3. We would kill the little add and transition.
Final Phase: Sulfurus smash and Engulfing flames remain but are easier to avoid. The only change is he summons big rolling meteors which chase random player and must be kited around until they are hit, which then they change targets. Throughout the phase more will spawn and I think we had 4 out when we defeated him. How we tried to handle this is keep hitting the balls away from the raid until they targeted our Mage who would just blink kite them around all day. Other than that you just dps him until he's defeated.
A pretty challenging fight but pretty simple once you master the mechanics. We didn't actually realize we beat him when our achievements popped up and he disappeared. We were like "huh, did we bug him or something?" but nope we just didn't know he was defeated once he hit 10% and felt cheated by how anti-climatic it was lol.
