Now that I've had a chance to play around with it, here is some more info and tips regarding the Infernal Machine event.
Drop RatesThe drop rates are the same for the Infernal Machine plans, keys, and demonic organs.
Remember, you must be in Inferno difficulty and you must have a stack of 5 Nephalem Valor (NV) in order for any of these items to drop!The drop rate itself is dependent on the level of Monster Power (MP):
Monster Power - Chance to DropMP0 - 5%
MP1 - 10%
MP2 - 20%
MP3 - 30%
.
.
.
MP10 - 100%
Note: Magic Find has no effect on the chance for these items to drop. (
Official Source)
Farming PlansThe plans for the Infernal Machine are dropped by
Nekarat the Keywarden in
Act 4 - Silver Spire Level 1. Start a game on the final quest (Prime Evil) and use the way points to travel to the
Gardens of Hope 1st Tier and
Gardens of Hope 2nd Tier and clear those areas. Once you have 5 Nephalem Valor, go to the
Crystal Colonnade waypoint and travel through the
Gateway to the Silver Spire to
Silver Spire Level 1 and search for the Keywarden.
Note: Once you find the plans you won't have to farm this Keywarden again.
Farming KeysIt's a good idea to start a game at the final quest of the act so that you have access to all the waypoints. Most of the time you will run into at least one elite pack in the area where you are searching for the Keywarden before you encounter the Keywarden so
you can usually get by with getting just 4 Nephalem Valor before going after the Keywarden. If you run into the Keywarden before getting your 5th NV just leave it alone and go to a different waypoint and search for an elite pack.
Key of DestructionDropped by: Odeg the Keywarden in
Act I - Fields of MiseryBuilding NV: Go to the
Festering Woods waypoint, it is a small area containing either two elite packs or one elite pack and one random event worth a point of NV. The area also contains two small sub-areas,
Crypt of the Ancients and
Warrior's Rest, which each contain an elite pack.
Key of HateDropped by: Sokahr the Keywarden in Act II - Dahlgur OasisBuilding NV: Go to the
Archives of Zoltun Kulle waypoint and clear out the sub-dungeons
The Unknown Depths and
The Storm Halls.
Note: Sokahr is the hardest Keywarden to find due to the size of
Dahlgur Oasis so this run tends to take the longest but you will usually run into a couple elite packs before you find the Keywarden so you can try starting the hunt with 3 NV.
Key of TerrorDropped by: Xah'Rith the Keywarden in Act III - StonefortBuilding NV: Start at
The Keep Depths Level 1 waypoint and work your way backwards. You will often find a NPC named
Ironsmith Maldonado who will start the random event
Forged in Battle which is worth a point of NV. From there you can clear that area then go to the
The Keep Depths Level 3 waypoint and clear that area if you need more NV.
Farming OrgansWhen you have used the plans to create an Infernal Machine portal device you can open a portal by using the device in the
Heretic's Abode, located in the boarded up house behind Brother Malachi the Healer.
Note: The Infernal Machine portal device is destroyed after use.
Three organ pieces will be needed to forge the Hellfire Ring:
The Writhing Spine, which drops from King Leoric or Maghda in the Realm of Discord
The Devil's Fang, which drops from Ghom or Rakanoth in the Realm of Chaos
The Vengeful Eye, which drops from Siegebreaker or Zoltun Kulle in the Realm of Turmoil
Important! The Infernal Machine portal device will
open a single portal to one of three random areas where you battle a pair of bosses. Each battle has a chance to drop one organ (drop rate is the same as plans/keys detailed above). Since the portal that opens is random
it is optimal to use three portal devices in a single game so that you get a portal to all three areas.
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EDIT 11/11/12: Only one active portal can be open at a time. Once the bosses in the active portal are killed the next portal can be opened in the same game.