Hydra (Diablo III)

Hydra is a Fire spell used by s in Diablo III. It is a remake of the classic Sorceress spell of the same name.

In-game
Summons a single three-headed Hydra at the targeted location anywhere within approximately 60 yards (not necessarily within line of sight). Each head rapidly spits high-speed firebolts, causing 165% damage as Fire to the first enemy they hit (missiles have a limited range). All Hydra heads try, but do not have to fire at a single target. Costs 15 Arcane Power, and has no cooldown. Normally only one Hydra per Wizard can be summoned.

Hydra cannot be directly controlled, is unable to move, does not block path, and may not be targeted with any attacks and spells, only disappearing in three cases:
 * 15 seconds of its life expire.
 * Another Hydra is summoned, causing the old one to despawn.
 * The Wizard dies.

Attack Speed of Hydra depends on that of its master, and each head spits independently.

Hydra has a zero Proc Coefficient. In other words, Wizard will not gain any healing for Hydra's attacks, and these attacks will not trigger any 'on hit' special effects. In return, Hydra's attacks will not cause Wizard to take damage from the Reflects Damage monster affix.

Hydra will not attack Treasure Goblins beyond 10 yards of itself if those are not yet in combat.

Hydra is a popular kiting build spell, as it can attack independently from the Wizard, and regardless of its master's movement.

The Arcane Hydra version does benefit from the Temporal Flux passive skill to everything within the area of effect of each bolt, turning it into a very effective AoE DPS and Crowd Control turret.

Hydra is not applying shields from Magic Weapon (Deflection) on attacking, only doing it on cast.

Mirror Images can summon Hydras as well. With Serpent's Sparker wand and Duplicates rune, a Wizard could have as many as 10 Hydras active at a time (even though 8 of them would be fake and do little damage). Since then this combo was fixed and now Mirror Images can have only one summoned Hydra at the same time, whatever the Images' numbers.

Hydra's attack speed interval is reset if it is resummoned. In other words, spamming Hydra again and again with careful timing can increase its attack speed (at cost of greatly raised Arcane Power expenditure).

As Hydra exists for a limited time and attacks independently, it benefits greatly from Attack Speed.

Runes:

 * Arcane Hydra: damage increased to 205%, damage type changes to Arcane, and bolts explode on impact, hitting all enemies within 10 yards.
 * Lightning Hydra: damage increased to 255%, damage type changes to Lightning, and target is hit instantly, being unable to dodge the attack.
 * Blazing Hydra: initial damage of each firebolt reduces to 0, but bolts explode on impact, hitting all enemies within 10 yards. Each enemy hit suffers 155% damage as Fire over 3 seconds, stacking infinitely, but not renewed. Note that unlike the speed of Hydra bolts released, the damage over time does not scale with attack speed.
 * Frost Hydra: damage increased to 255%, damage type changes to Cold, but bolts are replaced with a 20 yard range, 120 degree wide cone.
 * Mammoth Hydra: Hydra only has one head, damage increased to 330% per tick, but missiles are replaced with a 40 yard long, 5 yard wide line of fire that deals damage over time to enemies within and lasts 5 seconds (that is, 1650% damage as Fire per breath). Multiple lines in one area stack, making Mammoth Hydra effective against immobile enemies.

Non-rune enhancements:

 * Fragment of Destiny (Legendary Wand): Your Signature Spells attack 50% faster and deal triple damage. You gain a Spectral buff whenever you land an attack with a Signature Spell. Hydra deals 25-30% increased damage for each Spectral stack. Max 10 stacks.
 * The Magistrate (Legendary Wizard Hat): Hydra periodically casts Frost Nova and deals 250-300% increased damage. This Frost Nova DOES benefit from any enhancements of a regular Frost Nova spell.
 * Serpent's Sparker (Legendary Wand): two Hydras can be summoned at once, and Hydra deals 250-300% increased damage. Each new cast will cause the oldest of the earlier summons to despawn.
 * Tasker and Theo (Legendary Gloves): increases Hydra attack speed by 40-50%.
 * Winter Flurry (Legendary Source): increases Hydra damage by 125-150% to enemies in a.
 * Enforcer (Legendary Gem): increases damage by 15% (+0.3% per rank).
 * The Typhon's Veil (Set Bonus for 2 pieces): Doubles the duration of Hydras and increases the number of heads on multi-headed Hydras by two.
 * The Typhon's Veil (Set Bonus for 4 pieces): Damage taken is reduced by 8% for each Hydra head alive as long as there is one available. Taking damage causes one Hydra head to die, but no more than one every 2 seconds.
 * The Typhon's Veil (Set Bonus for 6 pieces): Hydras deal 2000% increased damage for each Hydra head alive.

Development
Originally Hydra was assumed to have a variety of rune choices involving the fully-functional summonable pet with the Striking rune.

Before patch 2.0., a Venom Hydra variant existed in game in addition to other types. It was removed along with all other variations of Venom and Blood magic from the Wizard's arsenal.