The Hell Forge is an object that is located in the River of Flame (Act 4). The location changes every now and then, but you can always locate it at the tip of a peninsula. You must defeat Hephasto the Hellsmith, who is located near the Hell Forge, and then take his hammer to complete the quest.
The name of the quest is Hell’s Forge, and you can trigger it by entering the River of Flame or completing the first quest of the act. The quest is handed over by the NPC named Cain, and the Hell Forge is located in the River of Flame for hell’s forge.
When you smash Mephisto’s Soul Stone on the Hell Forge, it’ll drop four random gems: 1x Normal, 2x Flawless, and 1x Perfect. The expansion also adds a dropped Rune per game, and the rune is randomly selected from the following ranges – Normal: El (r01) – Amn (r11), Nightmare: Sol (r12) – Um (r22), and Hell: Hel (r15) – Gul (r25).
It’s an optional quest, but since the rewards are good, it’s worthwhile. It was often skipped in the earlier patches as Hephasto was fierce, but it’s much easier in the Diablo 2 Resurrected.
You need to destroy the Soul Stone that you get from Mephisto. The stone needs to be taken to the Hell Forge, which is a blacksmith’s forge in hell and then be smashed to pieces. It’s the forge Izual attacks to prevent the completion of Shadowfang in Diablo mythology.
At the Hell Forge, you’ll encounter Hephasto, a unique monster that needs to be killed for a Hell Forge Hammer drop. You need to first click on the Hell Forge with the Soul Stone in your inventory, cute, or stash, for it to appear on the forge, and then equip the hammer, followed by clicking on the forge again. With a total of three swings, the Soul Stone will shatter to pieces.
The visuals are pretty good as hundreds of skeletal souls fly into the sky, which means they’re free as the stone was shattered for hell’s forge. The rewards are in the form of gems, as well as a rune. The four gems will fall to the ground as the souls fly away for diablo 2 hellforge. You obtain four gems for every player in the party who finishes the quest. However, the Rune that is dropped will only be one, no matter the players in the party, so make sure that you get it for yourself.
Hephasto was one of the most dreadful monsters in the game (in the earlier patches). He was known to be cursed with immense damage dealing power, magic resistance, and enhanced movement speed. He could easily catch up with most speedy characters, and he was packed with one-hit combat skills.
Even elite players were terrified to approach the River of Flames, as the exploration of the dungeon can trigger its spawn. He’s much easier in the new expansion, with Conviction and Spectral Hit replacing his previous Monster Modifiers. He’s not even that quick anymore, so it won’t take long to defeat him.
You don’t need to carry around the Soul Stone from Mephisto in act 3 because Cain will hand you a new one every time your approach him (if you don’t already have one) for D2R hellforge.
If you’re approaching Hephasto with Ranged, then you can lure him to a nearby lava spot that has a gap, so that he won’t be able to move around. After that, you can switch to the other side and defeat him from a distance for D2R hellforge.
If you’re a melee class character, you’ll benefit a lot from Stuns or Knockbacks, either in the form of a skill or equipment for diablo 2 hellforge. A good piece of advice would be to equip Cleglaw’s Pincers or utilize Bash/Smith to pin Hephasto against a wall and make him motionless. After that, it’s up to you.