Maybe tone it down a bit, give him like 6-8 abilities, but make the abilities choose a random timer from a set of, say, 12-16 different ones. Of course two abilities cannot hsare the same timer, so broken combos of insanity would (propably) not occur. One should also make sure that all those abilities were somehow avoidable. Let's say he'd have abilities like this;
1) Void zone thingy. Move out before it goes of.
2) Ki blast. A line is drawn one the ground, away from boss, and 5 seconds after he shoots cone (with a really sharp angle so it doesn't spread too much) centered on the line that'll propably one-shot anyone.
3) Barrage. targets 3 people in 10m, 8 in 25 man with a exploding missile. Lands where they were standing, avoidable. Doesn't one-shot, but does heavy damage so you do not want to get hit more than 1. (and yo cant stay spread because you need to be voiding his other abilities)
4) Boss does reduced damage (an amount that would make him pack a punch but not one-shot clothies), picks a new target randomly every 3 seconds and has 1000% (you read that right) increased movement speed.
5) Creates a shield on his other side that reflects spells. His other side will get an electric field that'll heavily damage melee attackers.
6) Lifts 3 people in to the air, tosees them into the closest wall and flings bombs as in ability 3) at them with his other hand. If the get hit by bombs, they are dead, dead, DEAD. (when he reaches enrage timer, he does this to the entire raid, hitting the wall will stun everyone, 25 bombs into the face, Ib/bubble/DI/whateva can still be used to try those desperate last percentages)
7) Kicks the tank in the nads with such a force it lifts him in the air, the punches him in the stomach while he's still in the air, smashing him to the wall, and throws a bomb, with triple damage, after him. Does soemthing gimmicky to his aggro, so offtank needs to pick it up.
I'll leave it at this as it'll propably be nicely hectic allready, and i like number 7. Now just make up a bunch of timers, split them to "short timer" and "long timer" groups, and flag some of the abilities to be able to pick from both lists while restricting some of the ebilities to "long timer" list. This way, you won't end up doing tank switch every 5 seconds, for example.
I'd fight this. And I tihnk I would have fun doing it.
Oh, and he HAS TO BE A GNOME.