Diablo III- Skills Article CXXXXI: The Wizard, Force Skills- Hydra

Hydra (15 Arcane Power): A three-headed hydra erupts from the ground at the target location, spitting bolts at nearby enemies that deal 28% weapon damage as Fire damage when they hit.  This hydra lasts 15 seconds, and is destroyed if you use the skill to create another Hydra.

An oldie but a goodie, Hydra is useful not for recastability, as you are only allowed one at a time, but for an incredible degree of Arcane Power efficiency.  The cost of it is tiny, and it sits for quite a while, regularly spitting out attacks.  If you use Hydra, make sure that you have another skill to resource-dump into.  The most difficult part of Hydra is choosing where to locate the heads- if they are too far from enemies, they will stop attacking, but if they are close to too many enemies, you’re likely to kill all of those enemies anyway long before the skill’s effect runs out, and it won’t focus its damage very well.

Arcane Hydra (15 Arcane Power): A three-headed hydra erupts from the ground at the target location, spitting miniature Arcane Orbs at nearby enemies that deal 28% weapon damage as Arcane damage to all enemies in a 3-yard radius when they hit.  This hydra lasts 15 seconds, and is destroyed if you use the skill to create another Hydra.

Arcane Hydra is a nice upgrade to the regular Hydra, replacing the unfavorable Fire damage type with a less-resisted damage and causing the attacks to become more effective against massed enemies.  This form of Hydra is best dropped into the middle of a cluster of enemies for maximum area-of-effect shenanigans.

Lightning Hydra (15 Arcane Power): A three-headed hydra erupts from the ground at the target location, spitting electrical bolts at nearby enemies that deal 34% weapon damage as Lightning damage when they hit.  This hydra lasts 15 seconds, and is destroyed if you use the skill to create another Hydra.

If you need more damage and a better type out of Hydra and don’t care about area of effect attacks or other tactical considerations, this is probably your best rune for the skill.  Lightning Hydra has higher raw damage than any other form of the skill, and a good damage type.

Venom Hydra (15 Arcane Power): A three-headed hydra erupts from the ground at the target location, spitting acid at nearby enemies that creates acid splashes on the ground which deal 18% weapon damage as Poison damage every second to enemies who stand in or walk on them.  This hydra lasts 15 seconds, and is destroyed if you use the skill to create another Hydra.

Venom Hydra is one of the two highly tactical forms of Hydra, creating a large number of small zones of continual damage.  Coupled with movement restriction, the damage can quickly exceed that of the regular Hydra, though if nothing is done to slow enemy movement, Arcane Hydra will deal more damage more reliably.  This one really depends on the other skills you put with it.

Frost Hydra (15 Arcane Power): A three-headed hydra erupts from the ground at the target location, spitting short cones of cold that deal 31% weapon damage as Cold damage to enemies in their area of effect.  This hydra lasts 15 seconds, and is destroyed if you use the skill to create another Hydra.

The other tactical form of hydra, Frost Hydra goes in the middle of enemy formations and slows them by dealing out Cold damage.  While the slow doesn’t last very well, being only the natural side effect of Cold damage, it is worth noticing and can help you keep things clustered up, especially if they have to cross the Frost Hydra’s reach to approach you.  The range is much worse than any other Hydra, though, so don’t use it if you keep your enemies spread out.

Mammoth Hydra (15 Arcane Power): A three-headed hydra erupts from the ground at the target location, belching streams of fire at nearby enemies that deal 22% weapon damage as Fire damage every second to enemies in their area.  This hydra lasts 15 seconds, and is destroyed if you use the skill to create another Hydra.

The Mammoth Hydra goes along with the Venom and Arcane Hydras as a way of getting area of effect damage into your Hydra.  While it retains the Fire damage typing, the damage is in the form of continuous streams, so it’s a good option to have when you have a single enemy that you can slow or stun while it’s near your Hydra.  It also functions well as a damage zone to force enemies into crossing, whether slowed or not.