Frost Mage

Frost playstyle is rather simple in that the most obvious choice is usually right. Right now, the spec has no real complexity, so achieving maximum performance with it is relatively simple due to the talent balance, which favors passive choices. Should you choose to play with Water Elemental or Rune of Power for example, the playstyle changes to a more intricate one.

Basic mechanics

Frost has very few spells in its arsenal, but there are some inter-workings which may not be instantly obvious.

First, when you have a Brain Freeze proc your Flurry is instant and applies Winter’s Chill to the target, which makes it so your spells count as frozen on it for the duration. The travel times of your spells are such that if you have a Brain Freeze proc, cast a Frostbolt and a Flurry right after, the Frostbolt will land after the first Flurry bolt, which means that it will benefit from Shatter. Obviously, you want to follow it up with Ice Lance, to take advantage of the short Winter’s Chill window. The same mechanic applies to Ebonbolt.

Another hidden mechanic is that the Brain Freeze proc has a slight grace period, meaning that as long as you consume the old Brain Freeze within a short time of the new one proccing, you will still get the new proc. This allows you to, for example, cast Ebonbolt while you already have a Brain Freeze and still benefit from both, as long as you press Flurry right after the Ebonbolt.

Single Target

With Thermal Void, the playstyle consists of using Ebonbolt and Frozen Orb on cooldown, syncing it with Icy Veins, if it’s about to come off cooldown (up to 20 seconds for Frozen Orb). Proper proc management is very important, especially during Icy Veins, thanks to Thermal Void.

Other than these 3 cooldowns, the rotation consists of spamming Frostbolt while using all the Brain Freeze and Fingers of Frost procs that you get. As noted above, the proper usage of Brain Freeze is to cast a Frostbolt, use the Flurry and then follow it up with an Ice Lance. When Fingers of Frost procs, you simply use an Ice Lance as soon as you can, which will most likely be after your next Frostbolt. Obviously, it may happen that you get both Brain Freeze and Fingers of Frost at the same time, at which point the correct thing to do is the Brain Freeze combo, unfortunately forgoing the Fingers of Frost. 

With Glacial Spike, the basic rotation remains the same, except you should now also track your Icicle count. Be aware of the fact that due to Ice Nine trait, you have a 20% chance to generate two Icicles instead of one. In 7.2.5 it’s possible for Glacial Spike to benefit from Winter’s Chill from a Flurry that you cast right after it, so for this reason, you should start saving any Brain Freeze proc from 3+ Icicles for the Glacial Spike. However, do not delay Glacial Spike if you don’t get a Brain Freeze.

Opener Sequence

1. Potion of Prolonged Power
2. Precast Frostbolt
3. Activate Icy Veins and Time Warp if you can
4. Ebonbolt
5. Flurry
6. Ice Lance
7. Frozen Orb

And from here on you deal with the procs as they come.

AoE

AoE is the biggest weakness for Frost, however, when there is more than 1 active enemy, you will want to use Blizzard on cooldown, mostly thanks to the Frozen Orb cooldown reduction rather than Blizzard’s damage itself. Keep in mind that thanks to Freezing Rain, your Blizzard will be instant for the duration of the buff. This duration is shorter with more haste, but it should almost always guarantee two instant Blizzards if you use them as soon as you can (exceptions exist, such as losing or gaining a haste buff).

Since Frozen Orb slows down at the first enemy it hits, you should try to position yourself such that it will hit as many enemies as possible right away.

You will also gain some damage thanks to Splitting Ice usage.