Firestorm is a fire attack used by Diablo which is like a more powerful version of the Druid's Firestorm Skill. It is also available for player characters, but only as a proc, from the Hellfire Torch.
Diablo typically casts Firestorms at somewhat close range, even though it will travel much farther than the deadly Red Lightning Hose. It is fast moving and tends to cover a wide path with random movement, making it a little difficult to outmaneuver, but quickly running perpendicular to its direction of carnage will often prove successful. Minions, however, are easily caught by the attack and killed instantly, making their usefulness, even as decoys, rather short-lived. It is advisable for Necromancers to draw some of the monsters which appear when the Seals are activated near this area before killing them, to ensure a supply of corpses nearby, for the use of Corpse Explosion.
Damaging Skills
Fire — Fire Arrow • Fireball • Fire Bolt • Fire Hit • Firestorm • Fire Wall • Flame Circle • Hydra • Incineration Nova • Inferno • Meteor
Ice — Arctic Blast • Blizzard • Cold Touch • Fire Hit (Cold) • Freezing Charge • Glacial Spike • Hoarfrost
Poison — Poison Bolt • Poison Breath • Poison Cloud • Poison Spit • Poison Spray • Poison Sting • Poison Strike
Lightning — Lightning • Lightning Arrow • Lightning Globe • Red Lightning Hose • Shocking Hit • Spark Defense
Physical — Blow Dart • Charge • Corpse Cannon • Destructive Strike • Ground Tentacle • Leap • Leech-life Ball • Quill Dart • Slam
Magic — Bone Spirit • Hellish Projectile • Unholy Bolt
Non-damaging Skills
Indirect Attack — Blood Mana • Curses • Mana Rift • Minion Frenzy • Putrify • Spin Web • Stun
Spawning — Bone Prison • Festering Appendages • Lay Egg • Revive • Summon Minion
Self-effect — Bone Armor • Burrow • Fly • Frenzy • Heal • Teleport • Vile Effigy