AoE Grinding can be achieved as a Mage through multiple methods. The most known Method is using Frost Nova to root mobs in place and to burn them down with Imp. Blizzard. Another method is to Flamestrike -> Nova -> Arcane Explosion mobs down. Another method is to kite mobs around with simple Cone of Cold rank 1 fishing for Clearcasting procs then using higher ranks of CoC or Blizzard. There are multiple ways to open an infinite value loop as long as your mana permits.
Here is a sample breakdown of a potential AoE Grinding Rotation GCD by GCD:
Pull: If 40+ Start Mounted up with Ice Barrier On. If you are under 40 then Face Pull / Wand / R1 Fire Blast to gather targets.
Control: Once gathered, use Cone of Cold to Slow all mobs and if any resist immediately use Frost Nova as a backup.
Create Space: Start Strafing Away or Blink Away to Create Distance (Ideally don’t Blink as the mana cost scales).
Kill: Use 2x Blizzard as they waddle in your direction and rinse and repeat using CoC or Nova to Control:
Tips & Tricks
When surveying a new area to AoE grind try killing a single mob with your combo to get a sense of its power level. If you are able to kill the mob in 4 Blizzards or less you are probably in good shape.
Use your Wand / R1 Fireblast to gather mobs that are spread out. Get creative with your positioning to gather them within range of your Frost Nova.
Do not pull packs of mobs with even a SINGLE ranged damage dealer. Always surgically dispatch of caster mobs first before starting your pull. Even a single attack can ruin your Blizzard costing you a ton of mana and potentially your life because you no longer have the resources to kill the pack.
Absolutely NO Frostbite talent. This will mess you up in a huge way freezing mobs randomly out of range of your Novas and Blizzards. You have to commit to either the Single Target Spec or the AoE Grinding Spec.
If after your 2nd Blizzard Mobs are closing the distance and Frost Nova isn’t fully off of CD use Cone of Cold to create more space. Keep strafing away for the couple seconds you need for a new Nova.
Generally you shouldn’t use Ice Armor as the slow effect will mess up your timings, however, if you are having trouble surviving you can use it as well as Mana Shield to increase survivability at the expense of efficiency.