{{template:quests}}Act Four takes the player into the depths of Hell itself, in pursuit of the greater evils. This act was designed as the conclusion of ''Diablo II'', and is about half the size of the first three acts. In D2X it's merely a stepping stone on the ultimate path to defeat [[Baal]], but still features one of the most dangerous areas in the entire game, in Diablo's [[Chaos Sanctuary]].
=Act Four: The Harrowing=
The goal of Act Four is to kill [[Diablo]]. In ''Diablo II '' this ends the game, in the Expansion it allows you to advance to Act Five. There are only three quests in Act Four, and it's the smallest of the Acts, with just five areas and no extra dungeon levels. The first two quests are optional, but the first has the best quest reward in the game, so you'll want to be sure to do it.
* '''Triggered By:''' Entering the Pandemonium Fortress
* '''Location: '''Find Izual in the Plains of Despair
* '''Quest Priority:''' This quest is not mandatory, but the +2 skill points is probably the best quest reward in the game.
Once you start Act Four, [[Tyrael ]] will have the "!" over his head, and want to talk. He tells you that there is a tortured soul, [[Izual]], the fallen angel, and you must find him and free him.
[[Image:Act4-012lrg.jpg|frame|right]]Izual will be found somewhere roaming around the Plains of Despair, the second area in Act Five. He is a relatively easy kill, as he has just a Cold Nova attack and a slow physical attack. The challenge is that he has an incredible amount of hit points, more than Diablo even, so takes quite a while to beat on. He's worth a good chunk of experience though, in addition to Tyrael giving you two skill points when you return to town after killing "Izzy" as he's called.
==Quest Two: The Hellforge==
[[Image:Quests-a4-q2.gif|right]]* '''Quest Name:''' The Hellforge
* '''Triggered by:''' Completing Quest One, or entering the River of Flame
* '''Given by:''' Cain
* '''Quest Priority:''' Optional quest, but a good reward. It was frequently skipped in v1.08 and earlier since Hephasto was so fierce. In D2X it's much easier and has a better quest reward.
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, which you must Identify it, and should then you can equip it.(It must first be identified in early versions of ''Diablo II''.)
[[Image:Act4-029lrg.jpg|thumb|333px|right|Break soulstone to release souls.]]If you click on the Hellforge and have Mephisto's Soulstone in your inv/cube/stash, the stone will appear on the Hellforge. Equip the Hellforge Hammer and click on the forge. It takes three swings to shatter the soulstone. You get a very pretty display as hundreds of skeletal-souls fly up into the sky, freed by the shattering of the gem.(The graphics are borrowed from the Paladin's little-seen [[Paladin_Defensive_Auras#Redemption|Redemption skill]].)
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.