Geleb Flamefinger casting Hydra.
This skill is used by the Council Members encountered in Act III and even in The Worldstone Chamber in Nightmare and Hell difficulty. It behaves in every way like the Hydra created by a Sorceress. It summons a three-headed beast which fires a volley of Firebolts.
Note, however, that the Council Members will also cast lightning simultaneously while summoning their Hydras.
Though a lone hydra is not so deadly, it can be annoying. However, Council Members are encountered mostly in groups who summon many hydras at a time which can cause serious trouble to players with poor fire resistance. It is generally a good idea to lead the Council Members away from that area and engage them once you are out of the range of the Hydra's projectiles.
In Diablo IV, it is used by the Hatred's Embrace apparition boss. Here, the 3 heads emerge in a triangle around the player.
Damaging Skills
Fire — Apocalypse • Eruption • Fire Arrow • Fireball • Fire Bolt • Fire Hit • Firestorm • Fire Wall • Fissures • Flame Circle • Flaming Skull • Grenade • Hydra • Incinerate • Incineration Nova • Inferno • Meteor • Minefield
Ice — Arctic Blast • Blizzard • Cold Touch • Fire Hit (Cold) • Freezing Charge • Frost Bolt • Frost Blast • Glacial Spike • Hoarfrost • Ice Shards
Poison — Poison Bolt • Poison Breath • Poison Cloud • Poison Spit • Poison Spray • Sting • Spew
Lightning — Discharge • Lightning • Lightning Arrow • Lightning Globe • Lightning Storm • Red Lightning Hose • Shocking Hit • Spark Defense • Thunderbolt • Thunderstorm
Physical — Bite • Blast Wave • Blow Dart • Charge (Berserk Charge) • Cleave • Corpse Cannon • Destructive Strike • Divebomb • Grab • Ground Spikes • Ground Tentacle • Leap • Javelin • Leech-life Ball • Pummel •Quake • Quill Dart • Roar • Screech • Slam • Snatch • Spectral Slam • Spine Dart • Strike • Swipe • Sweep • Whirlwind
Wind — Cyclone • Gale • Gust • Tornado
Magic — Beam • Blade Beam • Blast • Bomb • Bone Spirit • Cataclysm • Hellish Projectile • Nova • Slow Time • Tide • Torrent • Unholy Bolt • Volley • Wave
Non-damaging Skills
Indirect Attack — Blood Mana • Curses • Mana Rift • Minion Frenzy • Putrify • Spin Web • Stun • Vortex
Spawning — Bone Prison • Festering Appendages • Lay Egg • Minefield • Mystifying Growth • Revive • Summon Minion • Totem
Self-effect — Bone Armor • Burrow • Effigy • Fly • Frenzy • Heal • Shell • Teleport • Vile Effigy