Ray of Frost

Ray of Frost is a Cold spell used by s in Diablo III, seemingly inspired by Arctic Blast.

In-game
Ray of Frost forms an instant beam that hits the first enemy in its path, as well as other enemies within 5 yards of the target, for Cold damage per tick, chilling them down for as long as the beam is channeled. While the Wizard continues channeling the beam, its damage grows by 405% damage as Cold per tick, reaching maximum output over 2 ticks, normally 2 seconds (1240% as Cold per tick). Stopping the channeling will reset this bonus.

The beam has limited range, roughly 50 yards, and while channeling, the Wizard cannot move.

It is the only Wizard direct damaging skill that cannot change its damage type.

Runes:

 * Cold Blood: Arcane Power cost is reduced to 11 per tick.
 * Numb: slowdown increased to 80%, adds 10% chance on hit to Freeze affected enemies for 1 second.
 * Black Ice: killed enemies leave 5 yard radius pools of black ice, dealing 1625% damage as Cold to everything within it over 3 seconds.
 * Sleet Storm: beam turns into a radial storm. It affects all enemies within 15 yards of the Wizard, growing to 22 yards in 1 second, but damage is reduced to 300%, and damage buff from channeling decreases to 220% per second, to a maximum of 740% damage as Cold per tick.
 * Snow Blast: enemies hit by Ray of Frost suffer 15% more damage from Cold for 4 seconds, effect does not stack.

Non-rune enhancements:

 * Taeguk (Legendary Gem): increases damage done by 2% per tick (+0.04% per rank) and armor by 2% per tick (rank 25 bonus), stacking up to 10 times.
 * Light of Grace (Legendary Source): Ray of Frost pierces through enemies, hitting all targets standing in line, each of them forming a separate blast.
 * Mantle of Channeling (Legendary Pauldrons): while channeling Ray of Frost, increases damage done by 20-25% and reduces damage taken by 25%.
 * Deathwish (Legendary Sword): while channeling Ray of Frost, increases damage done by 250-325%.
 * Etched Sigil (Legendary Source): for every second of channeling, will also cast Energy Twister at the same target, and increases damage of Energy Twister by 200-250% while channeled.
 * Hergbrash's Binding (Legendary Belt): reduces Arcane Power cost by 50-65%.

Development
Before patch 2.0, Ray of Frost was a single-target spell. Snow Blast used to grow in power over time instead of increasing damage taken by the target.

Prior to Patch 2.1, it did not have a channeling-based buff.

Trivia

 * Seemingly inspired by this skill, Ray of Frost reappeared in World of WarCraft as a Mage talent.