XT-002 Deconstructor is the final boss in the SIege of Ulduar. And it may be suprising, but he's not actually that difficult. In terms of understanding a boss, positioning a boss, and dealing with his attacks, ol' Deconstructor is fairly straight forward.
Deconstructor actually really only has a few things to worry about. We'll cover those first, and then go into managing his phases.
Tympanic Tantrum is the first of Deconstructor's tricks. You can't miss the visual effect or cast bar when it starts. It hits everyone -- everyone -- in the raid for 10% of their total health every second for 8 seconds. That's when your healers have to be on the ball, and start getting heals out to the raid. If you have a cooldown that helps you mitigate damage, this is what you want to use it for.
Deconstructor's second significant trick is his adds. Periodically, little Scrap Bots, Bomb Bots, and Pummelers will come from the corners of the courtyard. Which corners they come from is random, and obviously more come during Heroic raids than during normal. Pummelers are your standard melee mob, and can be easily tanked. Scrap Bots will heal Deconstructor if they reach him, and Bombs blow up for AE damage when they reach the boss.
Deconstructor also uses "Light Bombs" (actually called Searing Light) and Gravity Bombs. These are raid killers, if the people who get hit by these abilities don't get away from the raid. If you get a Light Bomb, you need to be 10 feet away from anyone else, or you'll do periodic damage to them. If you get a Gravity Bomb, you need to be 30 feet away from anyone else when the timer is finished, or you'll drag everyone to you as if you head a multi-target Death Grip.
The last thing about Decontructor you want to know ahead of time is that he occasionally "powers down," and lowers his heart out of his chest. You can target it as a separate mob. When this happens, hit his heart -- it does a lot of extra damage when Deconstructor returns to his normal phases. That's the target you want to use your offensive cooldowns again.
So, let's bring this all together. When you enter the room, it's basically a big square. Have your tank hold Deconstructor up against the stairs, facing away from the raid. Blow him up. Have your melee clump up immediately behind him, and your ranged clump up a little further away. If someone gets a Light or Gravity bomb . . .get away from the raid!
When adds come, have your ranged characters kill them. Obviously, keep a distance from the Bomb Bots. Your offtanks should grab the Pummelers, and return them to the "melee" area. If you have sufficient AE melee fighters using things like Consecrate and Whirlwind, that "splash" damage and the damage from the offtank will kill them easily.
When the heart drops, kill the heart. When the Tympanic Tantrum starts, throw raid heals.
This fight can take a little practice, because people who get hit by the bombs need to get a little practice in getting the heck away. But other than that, this fight is pretty much cake. I actually found it much easier than Ignis, which required a lot more raid-as-a-whole movement.
Ready Check is here to provide you all the information and discussion you need to bring your raiding to the next level. Ready Check appears twice a week, with writers Jennie Lees and Michael Gray.