The Infernal Machine is an end game quest feature introduced in the v1.0.5 patch. The feature was teased pre-patch in several developer blogs ^[1] and interviews^[2] ^[3], which gave only vague details and hints about the content and creation of the feature.

First Description

The first word of the Infernal Machine came in a Patch 1.0.5 Sneak Peek developer blog post on September 13, 2012 ^[4]. The brief quote is below:

New Event: Infernal Machine
The Infernal Machine is a device that will allow level-60 players to battle “uber” versions of some of Sanctuary’s most nefarious bosses. While the rewards for defeating these bosses will be great, some assembly is required.

More information was released in a pair of developer interviews with Jay Wilson and Wyatt Cheng, posted on IGN^[2] and gnn.gamer.com.tw^[3].

As this is only available on the PTR expect that things may change before Patch 1.0.5 rolls out on the live servers.

Find the Keys and Plan

To unlock the Infernal Machine players have to gather 3 keys and a plan from all four acts by killing the Key Wardens. (An even longer and more involved process than Diablo 2′s Pandemonium Event.)

The Key Wardens always appear in an Inferno game but it is not guaranteed they will drop what you need.

However, you can guarantee a drop by utilising Monster Power. Each monster power level gives a 10% drop rate, therefore Monster Power 10 will give you a drop rate of 100%. Finally, you need to have five stacks of Nephalem Valor in order for the keys or plan to drop.

The drops required to assemble the machine are found in:

Key of Destruction	Key of Hate	Key of Terror	Infernal Machine Plan

Odeg in the Fields of Misery, Act 1	Sokahr in the Dahlgur Oasis, Act 2	Xah'Rith on theStonefort, Act 3	Nekaret in Silver Spire, level 1, Act 4

The Keys and Plan are Bind to Account so you can not trade for them. You can have more than 1 of each key at a time.

Build the Infernal Machine

Doorway to Hell

Once you have the three keys and the infernal machine plan visit the Blacksmith. He needs to be level 10 to craft the machine for you. He will charge you 12,000 gold. He will craft the portal device for you, which will sit in your backpack until you use it.

To use the device you need to go to the Act 1 quest Return to New Tristram (db) and locate Brother Malachi the Healer in the north east of Tristram. The house behind him has a boarded up door, smash it down and enter the Heretic's Abode.

Right click the device in your backpack and a red portal will spawn. This will lead to one of three realms where you will face two bosses you have fought before.

Realm of Discord - King Leoric and Maghda
Realm of Chaos - Ghom and Rakanoth
Realm of Turmoil - Siege Breaker and Zoltun Kulle

The machine will only work once and open one portal. To open another portal you need to reconstruct the machine again, by collecting the three keys, visiting the Blacksmith and paying him 12,000 gold to craft you another Infernal Machine device.

Rewards

The Bosses will drop loot but they also have a chance of dropping components needed to craft a special ring, The Hellfire Ring. The components are:

Writhing Spine drops from King Leoric or Maghda
Devil's Fang drops from Ghom or Rakanoth
Vengeful Eye from Siege Breaker or Zoltun Kulle

As with the keys from the Wardens you need to have 5 stacks of Nephalem Valor and each level of Monster Power will give you a 10% chance to drop the item, so MP10 gives you a 100% chance to drop.

The Hellfire Ring

You can buy the Hellfire Ring plan from Squirt the Peddler in Act 2 for 2 million gold. Take the plan to your Jeweler who needs to be level 10 and he will learn it. Once learned he will need all three of the above components and 50,000 gold to craft.

He can craft one of four varieties of the ring where one of the affixes will focus on Strength, Dexterity, Intelligence or Vitality. The stats are as follows:

Increase Bonus experience by 35%

Chance to launch an explosive ball of Hellfire when you attack (the proc on this has been greatly reduced since the PTR launched)

4 random properties

170-200 Intelligence, Strength, Dexterity or 100 Vitality (you choose with one)

The ring is account bound and therefore can not be sold or traded however it can be Salvaged.
You can only wear one Hellfire Ring, your Followers can wear one also.
There is no level requirement on the ring so any of your characters can wear it.