Peroth'arn:

Spread out, dps to his vanish. While DPSing he will Fel Flames one toon at a time. Just move them forward to backward a little and keep going. Alternative you could just have everyone move forward or back a little each time he casts it. When he vanishes, just have everyone follow and run around the edge of the ring. On the first try I got the achieve. If he catches one of you, have your tank taunt and do NOT restart DPS. He'll turn back to your slave again when the taunt runs out and kill them, so use your second taunt and you're golden. Alternatively you could just have your tank be the one that gets caught.

After the vanish wears off, it's the same as the first part. Spread out and DPS again avoiding Fel Flames.

Queen Azshara:

This was explained in the End Times post, but I'll somewhat repeat it here: Just make a line such that all your DPS can see the others and start killing the adds. Set the queen on focus and be ready to interrupt her very long wipe-cast. When you see the Arcane mage spinning, interrupt or stun it. If someone gets picked up, attack the strings. Otherwise, pretty simple... Almost like a trash pack.

Mannoroth and Varo'then:

Set your toons to follow and start killing Varo'then. When you see the Fel Firestorm, start running IMMEDIATELY. If you get caught, you will die. It is unhealable. Just avoid the flames and re-position. About half-way, Tyrande will get captured, so just kill the two big demons and go back to Varo'then. While she is captured though you need to pick up the other demons, but they don't hit hard. After Varo'then dies, just click on his sword.

Run to the far side of Mannoroth and start DPSing. Same thing for Fel Firestorm...just run around with your slaves following. When the demons start coming out, just have your tank pick them up. They don't hurt. Otherwise it's just a lot of spank without the tank.