Blizzard

Those familiar with Warcraft II or Warcraft III will recognize the classic mage ability, Blizzard. It deals its damage over 8 one second long ticks, each doing 1/8th the total damage. Like all channeled spells, the mana cost is deducted before channeling starts, so the full cost is paid regardless of how long you get/need to channel before the spell is interrupted or the target is dead. The spell is best used against crowds of targets that are not able to hit you to interrupt your channeling.

Background
This mage, wizard and sorcerer spell calls freezing sleet, snow and hailstones on foes. The cutting ice shards and hail pound down upon the caster’s enemies and foes, battering them and causing slashing, impact and cold damage.

Calling down shards of freezing ice to batter and rend their enemies, Archmagi have been known to rout entire armies using this spell. One of the Alliance’s most feared spells, Blizzard has become even more effective and deadly since its original inception during the First War. Summoning torrential storms from the frozen Mountains of Northeron, this potent spell calls down a fierce tempest of ice to assault the enemies of the Mage with a flurry of cold blades. Blizzard can be cast over large portions of the battlefield, making it an extremely powerful spell when facing legions of Orcish troops.

Talent improvements
Ice Shards adds a chill effect to all targets within the targetted area which reduces their movement speed to 60% of maximum at max rank. This effect lasts for 1 second after they leave the area or the spell is no longer being channeled. Permafrost increases the effectiveness of this effect to 50% maximum movement speed at max rank.

Impact from the Fire talent tree works with Blizzard. Because Blizzard deals damage in several ticks per casting, there is a high chance that Impact will proc, allowing you to stun one target with a Fireblast.

Arcane Instability, Molten Fury and Playing with Fire can increase the effective damage output of this spell.

Blizzard will apply Winter's Chill with each tick, when talented. Obtaining the talents Fingers of Frost and/or Frostbite, coupled with the talents Shatter and Improved Blizzard, will result in a very high critical strike rate for Blizzard, increasing its AoE potential vastly.

Precision and Frost Channeling reduce the mana cost of this spell, while Frost Channeling also lowers its threat. Blizzard deals Frost damage, so the bonuses from Piercing Ice, Ice Shards and Arctic Winds apply to the spell. Arctic Reach extends the range to 36 yards at max rank.

The Master of Elements talent will refund mana from Blizzard per tick that critically strikes. However, the returned mana is proportionate only to the tick that critically struck, and not the total amount of mana spent to cast Blizzard. Against multiple targets, the chance to strike critically is increased, though only one refund per tick will be produced. Nevertheless, this still allows mages to conserve mana with what is an expensive spell.

Tips and tactics
Some frost specialized mages will take Ice Shards and kite whole crowds of mobs relying on the snare effect to buy them enough distance to cast again.

A mage who invests in the Frost talent tree can combine Ice Shards and Permafrost to produce a Blizzard that effectively hinders the movement of targets. Blizzard's multiple ticks of damage give the Fingers of Frost and Brain Freeze procs several chances to take effect.

Most mages find this spell hard to cast fully in PvP. Because of the large number of debilitating procs on the spell, as well as the high damage output, many targets will immediately begin seeking out and subsequently killing the mage casting Blizzard. However, in large or confusing battles, or from sufficient cover, it may be possible to cast the spell to its conclusion, doing great damage and snaring the targets for the duration.

A single tick of damage from this spell is enough to reveal stealthed opponents and apply the snare; this can be useful in limited circumstances.

Farming and leveling with Blizzard
The Blizzard spell is - when upgraded through talents - a great tool to rapidly gain experience and to smash whole groups of mobs at once making it a powerful farming spell as well.
 * In contrast to fire-based AoE spells like Flamestrike Blizzard must be channeled. However it will nearly immobilize enemies (snaring by 85% if fully upgraded) and often freeze them in place.
 * When focusing on Blizzard +spell power is very useful. Increasing your spell hit chance will make it less likely that mobs resist single waves of Blizzard and hence reducing the danger of mobs breaking free of the slowing effect. Remember the base miss chance versus spells of mobs which are the same level as your character is 5% and can be negated by sufficient spell hit gear.
 * Taking the talents Fingers of Frost and/or Frostbite will make these effects trigger out of Improved Blizzard's snare. When coupled with the Shatter critical strike chance, Blizzard has a VERY high chance to critically strike. This is critical for maximizing Blizzard's potential, and can be further enhanced with Winter's Chill.
 * Ideal locations for this tactic have large numbers of mobs that have few or no ranged capability. These mobs will be caught in the snare and will stay packed together, walking very slowly towards you, as you continue to cast Blizzard spells.
 * Example: For levels near the range 49-55, the graveyard northeast of Chillwind Point in the Western Plaguelands, which has loads of skeletons and ghouls with no ranged attacks.
 * Example: The level 60 Scourge Siege Engineers found south of the portal to the Ghostlands in the northern part of the Eastern Plaguelands. Despite the variety of models used, they are all melee attackers with no special abilities.  Best of all, they naturally spawn close to each other, making it easy to position Blizzard over several mobs at once at the start of combat.
 * Example: The wrathbringers right after the entrance to Shadowmoon Valley have no ranged attack except their long-cooldown firewave and would be perfect targets if they were not mixed with Legion smithes that have a lot more hitpoints.
 * As blizzard is very expensive, maximize your effectiveness by attracting as many mobs as possible at once.
 * Ice Lance can help to gather mobs from a distance without exposing yourself (immediately, at least) to their melee attacks.
 * Ice barrier and your mount can help while gathering mobs together. Ice Armor may help or hurt; it keeps mobs off you while gathering, but may keep them from being close enough to hit with your blizzard.
 * If the cooldown is acceptable, Ice Block can be used after gathering mobs, causing them to all catch up to you and surround your invulnerable body.
 * Use Frost Nova (especially if you're using the Ice Block method, above) to freeze mobs you have gathered and gain some distance from them before beginning your blizzard casts. Alternatively, if you are able to get range through other means, save it to regain distance if your first casts do not kill your targets before they reach you.
 * At level 50 on you may use your water elemental as an additional freeze effect, usable at range to slow your targets' progress towards you.
 * If the mobs reach you before dying, use Frost Nova to regain distance. Alternatively, if they are low in health, a cast of Cone of Cold or a few Arcane Explosion casts may finish them off.