Twin Val'kyrs

The Twin Val'kyrs are a white and sort of dark purple pair of flying valkyries. Your job is to kill them.

Shopping list:
2 tanks
6ish healers
DPS

The mechanics are harder to explain than they are to do, and make a hell of a lot more sense once you have done the fight once.

Split your raid up into 2 even teams, left and right. By even, I mean a balance of ranged and melee on each side so make ability 1 below easier to handle (see comments for explanation from HairyHippy, RL extraordinaire!). Everyone can then edge up to the nearest coloured portal blob on their side of the room. You will see it is clickable, if you click it you will gain a foot aura of that colour blob, either light or dark. It is not a coincidence that these are the opposite to the val'kyr on your side.

Mark the twins up and engage. Pull them left and right, between the two coloured portal blobs on each side (more on those in a minute).

This is simply a DPS race. They share a health pool, so effectively you are fighting 1 boss with twice as many hit points, so it really doesn't matter who you are DPSing (this will become important in hardmode, I am sure). The one thing you have to remember is, you can only properly damage the Val'kyr who is the OPPOSITE colour to your foot aura.

Make sense? Look at your foot aura, and damage the Val'kyr of the opposite colour. There is one exception, but that is noted below. If, at any time, you need to change your foot aura, simply run to a portal blob of the colour you want and right click it. Easy! Foot aura changed!

Healers, it doesn't matter which colour foot aura you have, unless you plan on DPSing at any stage. Just plant yourself evenly around the room, parked near the OPPOSITE colour portal blob, ready for ability 3 below. That also goes for as many DPS as possible.

Ok now, the val'kyrs have a few special abilities and they are all to do with your foot auras.

1. Light or Dark Shield. Every so often one the Val'kyrs decides to put up a shield and the other goes apeshit crazy and duel wields. Everyone who is DPSing has swap, regardless of foot aura, to the val'kyr with the shield and smash through it or Bad Things(tm) will happen. On the apeshit dual wielding crazy one, healers need to pay attention and make sure the tank does not die. Pretty straight forward, just remember you need to move fast, that shield is up only for a limited time before Bad Things(tm) happen. If you get the shield down in time, you have the opportunity to interrupt the Bad Thing(tm). So make sure your interrupters are on the ball as soon as that shield is outDPSed.

2. Floating blobs! This can get confusing but if you remember same = good opposite = bad then you should be ok. Basically, if you collect blobs of the SAME colour as your foot aura, you get a buff. If you hit one of the OPPOSITE colour as you, you take damage. Bad Things(tm) happen if the val'kyr get the floating blobs. So, since in normal mode, the damage is easy enough to heal through, just mop them all up, with perhaps your big hitters trying to collect same coloured blobs.

3. Light or Dark Explosion!! At some point one of the val'kyr will go all Peter from Heroes on your arse, and set off a nuclear explosion of one of the colours. As they start casting, you have 8s to make sure everyone moves to the portal blob of the same colour. Click it!! Your foot aura has to be the same colour as the val'kyr going nuclear on your arse. One MAJOR thing to note here, do NOT crowd the blob portals... people may not be able to click them if everyone is standing on top of them. The clicking range is very large, so only go as close as you have to then move away. If you don't get to a portal in time, you will take 1 burst of the light or dark damage every second for 5s. Yes, it will kill you. This stacking contributed to one or two deaths in my raid when we did it.

That's about it. DPS the boss, deal with each of the special abilities above as they come. If you have come this far in ToC, this boss should be a piece of cake for most guilds once the coloured blobs are understood.