Here's a quick summary of the steps in this event. See the sections below for full details about everything related to the Infernal Machine.
- Obtain a key from each Keywarden.
- Diablo 3: Keys found from the Keywardens in Acts 1-3. Infernal Machine plan and/or a random key from the Act 4 keywarden.
- Reaper of Souls: Keys from Acts 1-4 in RoS, with one key from each Keywarden.
- Craft the keys (one of each required) to create an Infernal Machine.
- Enter the Heretic's Abode in Act One Tristram town.
- Activate the Infernal Machine(s) to open a red portal to one of the Realms.
- There is only one kind of Infernal Machine in D3, and the portal opened is random. Players are advised to have 3 Infernal Machines to do all three in the same game.
- There are 4 types of Infernal Machines in Reaper of Souls, so players can open precisely the portal they wish.
- Slay the Ubers in the realm, and cross your fingers for a Demonic Organ to drop along with the other loot.
- Once you have at least 1 of each type of Demonic Organs (3 in D3, 4 in RoS) visit the Jeweler to craft them into a Hellfire Ring.
It is usually necessary to repeat the initial steps multiple times, since keys and organs do not drop every time. Even on Torment 6 they have only a 50% chance to drop. Players can farm for the keys and organs much more efficiently in multiplayer games, both for the faster killing speed and since every player in the game has a chance at each item dropping, and all characters in the game can pass through the same portal(s) to the Uber battles.