Mimiron is a four-phase tier eight fight with some complex mechanics and a good deal of entertaining humor to it. In my opinion, the Ulduar raid was the crown jewel of Wrath of the Lich King, and Mimiron was one of the most fun and challenging bosses in it.
What made Mimiron particularly interesting was the way the four phases related to each other and, ultimately, combined. In phase one you fight a siege engine-style tank, in phase two a pair of mini gun-like cannons, in phase three a helicopter head, and then in phase four they all come together to make a giant, three piece robot - named V-07-TR-0N, of all things. Also, keep in mind that, being a Wrath-era boss, Mimiron had hard mode. And it was hard. More on that later.
Each phase had a specific set of mechanics to master. In phase one, you fight the Leviathan MKII, which has both AoE and single-target mechanics to watch out for. Plasma Blast ability can possibly one-shot a tank. In phase two, Leviathan is replaced with VX-001 Anti-personnel Assault Cannon. The Assault Cannon, like the Leviathan, also has a one-shot technique - but it is AoE this time, and can hit everybody. If you make it through phase two, you meet the Aerial Command Unit in phase three, which flies above the raid and needs to be tanked by a ranged class. Reminiscent of Lady Vashj's Tainted Core mechanic, during phase three there are add spawns which drop Magnetic Cores upon death. The Magnetic Cores must be looted and used underneath the Command Unit in order to bring it to the ground so that it can be DPSed more effectively.
Once you make it to phase four, all three of the units you just defeated assemble together - the Leviathan as the feet, the Assault Cannon as the body, and the Aerial Command Unit as the head. They have three different health bars and all three parts must die within 15 seconds of each other or they will self-repair and reset. The head is once again out of melee range, so good coordination was key - melee generally focused on the Leviathan, ranged on the ACU, and both work to DPS the Assault Cannon. Fortunately each part does not retain every single mechanic from their individual phases, however, the combined unit still packs plenty of punch.
If you could master all these mechanics and positioning, you could defeat Mimiron, and plenty of guilds could. The real test lay in defeating Mimiron's hard mode. The real test lay in earning yourself the Firefighter achievement. You unlocked Mimiron's hard mode by pushing the big red button at the back of the room, and then you're treated to Mimiron berating you for activating the self-destruct mechanism. Way to go, everyone! The encounter begins as soon as you press the button, and the first added mechanic is fire - lots and lots of fire.
Fires spawn on random people throughout the raid, and chase whoever is closest to the fire. Thus, the fires will follow the raid around the room. If positioning was important to Mimiron's normal mode, it's paramount in hard mode. There is a lot going on. As you can see in the video embedded above, it's easy at points for the fire to spread to a significant portion of the encounter space and severely limit the raid's ability to move around. This can pose a lot of difficulties in phases two and four especially, when the Assault Cannon is doing its Laser Barrage.
Oh, did we also mention that Mimiron's health and damage is increased by 30% during hard mode? Yeah, that too.
In phase two, Mimiron adds a Frost Bomb to his repetoir - it puts out fires on the ground, but does so via an explosion that does 50,000 damage. So even when something good is happening (fewer fires!) it can still kill you. In phase three, Emergency Fire Bots spawn and can also put out fires, but they too can deal some serious damage to the raid, and thus must be killed. The Magnetic Cores mechanic is still in effect, so you still need to worry about that. If you can make it through to phase four, it actually looks very similar to normal mode's phase four, except that fires still spawn, and Mimiron throws Frost Bombs. Those might actually be a welcome addition at this point, though.
For much of tier eight, "Firefighter" was a dirty word, not unlike "Kael'thas" in tier five. Firefighter is needed in order to proceed to the Algalon fight, and it was usually the biggest hurdle to overcome for a guild hoping to reach that final battle. Firefigher, along with Alone in the Darkness, remains one of the most infamous achievements from Wrath of the Lich King. Completing it at level and during its current tier was no small feat, and those who did it have every right to be proud of that achievement.
Here ends my mini series on best fights. I know we still have Cataclysm to cover, but alas I did not raid at all during Cataclysm, so I cannot write that article. If you want to see it, you'll have to bug another WoW Insider columnist, I'm afraid!