Changes

You must destroy the Soulstone you got from Mephisto on the Hellforge, a blacksmith's forge in Hell. This is the forge Izual was attacking to prevent the completion of Shadowfang when he was captured, in the Diablo mythology. At the Hellforge you'll find Hephasto the Armorer, a SuperUnique monster. You must kill him to make him drop the Hellforge Hammer. Once you have it, you must Identify it, and then you can equip it.

The reward is in the form of gems, and a rune in the Expansion. Four gems fall to the ground as the souls are flying away. They are always one normal, two flawless, and one perfect, of random types. There are four gems for each player in the party who is finishing the quest, so in a five player party, with three people needing the quest all in Act Four, you'd get twelve gems, and have to sort out who gets which. You want to be careful if you are new to Act Four, and in a party, since others might finish the quest and get all of your gems even if you are in another area. In the Expansion there is one Rune dropped each time the soulstone is smashed, no matter how many are in the party, so you might want to be sure you do the quest yourself to get your Rune.