Spec arcane. Gear for Hit > Mastery > Crit > Haste. Override your Arcane Missles glyph with Molten Armor glyph for P3. Spec Incanter's Absorption (you most likely won't be AoEing, ignore imp AE).

Our raid has to hold off on AoE because the whelps die way to quickly otherwise. By the time AoE starts, the whelps are all the way at the back of the room. It would not be worth standing next to them and AoEing, as you want to begin DPSing Sinestra's mana shield to make the eggs vulnerable ASAP.

Classes who have a ranged AoE can pad the meters and throw some AoE on the whelps while standing at the edge of the Fire Barrier near Sinestra, but Arcane has better things to do.

Other classes often do more total damage for the Sinestra encounter - however every time I check recount, I have always done the most damage to Sinestra herself (I don't cast a single AOE spell, there are other classes who do it much more efficiently).

I didn't think you could be in range of Sinestra and inside the Fire Barrier, by better things to do do you just mean positioning to move to your spot as quickly as possible?

It is certainly possible to be in range of Sinestra while inside the barrier.

On H Cho'gal as a frost mage (I had to do so for replenishment).

-You should time ice barrier and mana shield so that they will come off of cooldown during shadow's order. Doing this will almost completely mitigate the damage (with mage armor).
-I find that cold snap is best used for getting iceblock off of cooldown to mitigate two shadow's orders.
-Use a /castsequence macro so you will still cast FB, as using FFB is higher dps (to keep up replenishment).
-If you use your mitigation CD's correctly you should reach the execution over 75% health, allowing you to double dip in heroism (from the initial hero at phase start, then a personal time warp after you are brez'd).

On the Shannox fight, Rageface will focus on whoever breaks his Face Rage attack for about 15 seconds. With arcane's fast casts and direct damage, I ended up taking more than half of Rageface's overall damage for the fight. Switching to frost armor helps healers out a lot. As this is more of a survival fight, I think the loss of GCDs and mana is worth it.

While this may seem obvious to most, I did not think of it until someone mentioned how some of the threat issues would be similar to Bloodboil. Mages pretty much had to use frost armor to survive being focused by him.

You could glyph Frost armor (if you're playing arcane) to help out a lot if you're going to use Frost Armor

Just wanted to write that. Actually you should switch Fireball to Pyroblast at around 12stacks (depends on your gear haste) of haste (at this point fireball starts to suffer from gcd). Also LB is still good to use every time it wears off, cause its buffed by haste aswell.

One question tho, did anyone manage to keep their buff alive through the phase transitions? I still have it for the burn phase, but before I can fly up again I lose it.

It's not possible, unfortunatelly, due to her nuke-phase duration

Concerning the "Cho'gall heroic effect" on Alyzrazor, does it require Mage Armor?

edit: typo

Regarding Rhyolith Normal or Hardmode.

Rhyolith begins with a shield up which reduces all dmg taken by 80%. This drops as the encounter goes on and getting him to 25% is what begins P2

However, looking at logs seems to show that he takes combustion damage via impact spread without the shield mitigation.

The Spark of Rhyo is a great one to nuke (if you tank him with 12 yds of the legs) - build up a big ignite - then combust and spread. It's possible to have both legs ticking for 25k (normal) and 50k (crit) even early in the encounter with a large shield up.

Logs below to show his combustion ticks from a 3 min attempt from just 1 fire mage in raid:

World of Logs - Real Time Raid Analysis - left foot
World of Logs - Real Time Raid Analysis - right foot