Since this was going to be an off-week anyway, we went in on Tuesday to wrap up Halion - we had pretty much ignored him since his loot table sucks donkey balls. But people wanted the achievement and the one night we spent kind of swiping on him a few weeks ago got us kinda close a few times, I figured we could wrap it up.
So, with a couple of PuGs due to the low population week, we went ahead and pulled the mini-bosses who are pretty silly, and then worked on Halion.
Initially, I tried moving him in the Shadow zone, then moving at a 90 degree angle to the beams, then only moving when the cutters were active, then back to the other thing and after 3 or 4 tries I was getting an understanding of the movement but I wasn't exactly getting it nailed down.
That's when one of our PuGs mentioned that her guild pretty much just keeps the leading orb to the tank's left shoulder and has the rest of the raid in the open space to the right of the tank and that worked just brilliantly! We wiped once or twice again as people kept dying due to tunnel-vision but then, I think the fifth or sixth pull was the magic one, and down he went with great ease.
One thing to keep in mind when moving him this was is that a linear strafe won't work since you've got the Dragon in the middle of the room and are spinning him in a circle so you need to do a shuffle-strafe - move diagonally and up as well, I found it easier just to use my mouse to move. A shuffle/strafe would probably work but just manual movement worked fine for me.
I didn't try to toggle /walk either as some people did when they were tanking Grobbulus for example - I prefer to have my burst of speed and stop short at hand instead of crippling my movement. But your mileage may vary on that.
The only complication, I think, was balancing the damage in phase 3, and that was easy enough, whenever a second shift occurred, I had our Boomkin jump into the Shadow Zone to help bring him back down to zero.
At two shifts, I did have to start chaining CDs and at one point, I had to ask for healer CDs as well, and a single healer can easily keep the Fire zone up without a problem even with a 50/50 split. That leaves two heals to stay in Shadow Zone and they seem necessary just to cover the increased tank damage from the Twilight Radiance bullshit and also since he will very likely shift into shadow and do increased damage there since there are 3 DPS in fire and only 2 Shadow.
Once he was sub-10% I just had the boomskin stay in Shadow and as he started to shift into fire where our DK tank was easily able to chain his CDs until kill.
Not a bad fight, and interesting enough that I wouldn't mind killing him regularly if his loot-table wasn't so crappy. Ah, well.