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wowanalyzer.com Suggestions for a log

You should use Brain Freeze immediately following Frostbolt if you have fewer than 3 Icicles during the Frostbolt cast. If you have 3 or more Icicles during the Frostbolt cast, save the Brain Freeze proc for Glacial Spike.

icy-veins.com Frost Rotation Guide

Cast Flurry Icon Flurry if you have Brain Freeze Icon Brain Freeze and
you have just cast Frostbolt Icon Frostbolt and are currently at 0-3 Icicles OR;
you have just cast Glacial Spike Icon Glacial Spike.

alterd-time.com Frost PvE Guide

If you do have Glacial Spike talented, the usage of Flurry changes. Cast Flurry If you have 5 stacks of Mastery: Icicles after casting Glacial Spike, or if you have less than 3 stacks of Mastery: Icicles cast it after Frostbolt. If you will have >=4 Mastery: Icicles at the end of your Frostbolt cast you hold Brain Freeze for Glacial Spike.

So there seems to be some differing information about how to best use your Flurry procs when spec'd for Glacial Spike, and it may be that the difference is negligible, but what is the proper Icicle count to be using Brain Freeze procs? 0-2 or 0-3?

If you have 3 or more icicles, save your BF proc for GS

(Remember Flurry also generates icicles now)
If the Frostbolt + Flurry combo would put you at 5 icicles, don't do it.
If it puts you at 4 or lower, go for it.

Personally, it depends if I have Ebonbolt available or not.
If it's available and i'm at 3 icycles, i go for Frostbolt > Flurry > IL which gives me 5 icycles and then I go Ebonbolt > GS > Flurry > IL.
If it's not and i'm at 3 icycles, I just hold the proc for the GS inc.

They're actually all saying the same thing, just worded differently. Wowanalyzer is telling you to Flurry after a Frostbolt cast if you are at 0-2 stacks while casting the Frostbolt, while Icy Veins and Altered Time are telling you to Flurry after a Frosbolt if you're at 1-3 stacks after the Frostbolt. The Frostbolt that we're casting contributes to your stack, so 0-2 before the cast goes off is the same as 1-3 after the cast goes off.

IMO, the Wowanalyzer wording is better because you're never going to cast the Frostbolt and wonder, "Hmm, am I at 3 stacks now? I am, better cast Flurry." The timing window requirement of the Flurry cast requires you to know what you're doing before the Frostbolt finishes casting and it's more natural to look at your current count of Icicles. Not that mentally adding a stack is a difficult task, just unnecessary.