Diablo II/Hell's Forge

The second quest in Act IV can be activated first if you talk to Deckard Cain before Tyrael:

If you didn't pick up Mephisto's Soulstone when you killed him then Deckard Cain did so, and he gives it to you when you talk to him: it requires one inventory space.

Surprisingly, this 'crucial mission' is optional: as far as the plot is concerned, if you don't complete it then you must destroy Mephisto's and Diablo's Soulstones together (although killing Diablo first doesn't prevent you from completing this quest in a later game).

The Hellforge can be found in the, beyond the , and City of the Damned.

City of the Damned
The City of the Damned is randomly populated by three of the following seven monster types: s, s, lightning-spitting, roosting s, fire-breathing s, mana-draining s and s (which spawn s). There are also s, and there can also be corpse-spitting s, and s.

The stairs down to the River of Flame are somewhere in the City of the Damned, and there's a waypoint nearby.

River of Flame
The River of Flame is randomly populated by three of the following seven monster types: s, s (which spawn s, which in turn spawn ), s (which spawn s), corpse-spitting s, fire-breathing s, mana-draining s, and s.

The waypoint is always to the northeast, where the angel Hadriel guards the final approach to the entrance to the. If you talk to him before completing this quest:

However, he doesn't actually stop you from traveling beyond him to the Chaos Sanctuary.

The Hellforge is always at the end of a spur of rock to the northwest or southeast. Approaching it will trigger this quest if talking to Deckard Cain hasn't already done so:

At this point, you should start clearing the approach to the Hellforge before you encounter its guardian...

Hephasto the Armorer
../Demon/

Your soul shall fuel my Hellforge!

Hephasto needs to be killed, as he drops the Hell Forge Hammer required to destroy Mephisto's Soulstone upon the Hellforge. He has Poison Resist -50% in Normal and Nightmare, and none in Hell. Although not as fearsome as in earlier versions of the game, his aura may augment not only his own power, but that of any other monsters in its area of effect, and can still be useful to pin him against an obstruction or the shore of the river.

Hell Forge Hammer

 * Hell Forge Hammer
 * One-Hand Damage: 6 to 15
 * Durability: 55
 * Mace Class - Speed 0
 * Adds 5-20 Fire Damage
 * +35 Defense
 * Fire Resist +40%
 * +50% Damage to Undead

It requires 3x2 inventory space. After placing Mephisto's Soulstone on the Hellforge:

Equip the Hell Forge Hammer and strike the Forge three times to destroy Mephisto's Soulstone, releasing the souls trapped within. A selection of random gems drops from the Hellforge: one perfect, two flawless and one normal quality.

One of the following also drops:

If you talk to Deckard Cain: