Why doesn’t Fingers of Frost provide Shatter Combos?
Two big reasons: 1) No time pressure. The reason we use an instant cast in a Shatter Combo is because the choice is between an instant cast against a Frozen target or a Frostbolt against a non-Frozen target. With Fingers of Frost, that is not the case; because the buff is charged rather than timed, and the charges disappear on cast rather than on hit, flight time does not come into play; both spells will treat the target as Frozen, regardless of cast time. 2) Using a Shatter Combo produces less DPS than spamming Frostbolt. This becomes true at a fairly modest amount of Spell Power, somewhere in the 1700-1800 area. Partly it is due to poor scaling on the part of instant-cast spells. Partly it is due to the fact that no long-range instant-cast spells can proc Fingers of Frost or Brain Freeze. Basically, to make a Shatter Combo match the DPS of pure Frostbolt spam, an instant-cast spell needs to deal enough damage to equal 60% of a Frostbolt against a frozen target, plus enough damage to
