I've had this post ready for a couple of days waiting for the PTR update that included the change. Here's how the new Mastery works (some of this may have been laid out in official notes or datamined info, but I don't know as I'm writing this how complete they'll be).
Several other changes are being made in conjunction with the Mastery change:
- Frostbolt no longer increases its own damage. It still applies the debuff, and its own damage is not being increased. However, as you'll see from the Mastery information below, its effective damage is now being increased by the new Mastery.
- Ice Lance damage is being increased by 29%. If you previously had +40% Mastery, this works out to about an 8% reduction across the board. By comparison, the first PTR change to Frostburn would have not affected damage with FOF procs, but would have reduced damage vs frozen targets by about 29%.
- Waterbolt damage is being increased by 9%. Again, if you previously had +40% Mastery, this is a reduction of about 22%. But as with Frostbolt, see below for the way the new Mastery affects it.
Every Frostbolt, Frostfire Bolt, and Waterbolt that deals damage to a target now generates an Icicle of 1.5% the damage of the original spell per point of Mastery.
So say you have 20 Mastery. With Frostburn, this would have increased damage to frozen targets by 40%. With Icicles, it will generate Icicles that store 30% of the damage you deal with each Frostbolt, Frostfire Bolt, or Waterbolt.
You can store up to five Icicles. Each Icicle has an individual duration of 15 seconds. They are used in one of two ways:
- When you cast Ice Lance, you will immediately begin to discharge your Icicles. They will launch at the target the Ice Lance hit, at the rate of one per second (adjusted by haste), until they are gone.
- If you generate a new Icicle when you already have five, the oldest will immediately launch at the target hit by the spell that generated the new Icicle, and the new one will be stored.
A simple way to look at it is this: Icicles is like Ignite, if you were able to save up some Ignite damage and deliver it to any target on demand.