From Diablo Wiki
Keywardens are unique bosses who have a chance to drop the keys and plan required to activate the Infernal Machine and obtain a Hellfire Ring. Keywardens are only found on Inferno difficulty, and each one is randomly located in a given level, one per act.
To have a chance at one of the keys or the plan dropping, players need to kill the Keywardens with 5 stacks of Nephalem Valor. Higher levels of Monster Power increase the odds of a key dropping. Keywardens drop items like other Elite bosses, and can be a good source of legendaries and rares, but their special ability to drop keys is what makes them prized enemies.
All keys, the crafting plan, the Demonic Organs and the Hellfire Ring are BoA, which means they can not be traded for or even given away. Players must farm the ingredients themselves, though all players in a multiplayer game can use the portals to the various Uber battles.
- See the Infernal Machine article for full details.
 Obtaining the Keys and Plan
The Keywardens appear randomly-located in their special areas. Prior to v1.08 they could be found in all difficulty levels, but they now only appear on Inferno. To have a chance of a key dropping, a character must have 5 stacks of Nephalem Valor when the keywarden dies. (If a character does not have 5 stacks and sights the keywarden, the player needs merely leave him alive, get fully stacked, then return for the kill.)
The four keywardens and the planwarden are:
- The Key of Destruction may drop from Odeg the Keywarden in Act I - Fields of Misery
- The Key of Hate may drop from Sokahr the Keywarden in Act II - Dahlgur Oasis
- The Key of Terror may drop from Xah'Rith the Keywarden in Act III - Stonefort
- The Blacksmithing Plan and random keys may drop from Nekarat the Keywarden in Act IV - Silver Spire Level 1
The first three keywardens can only drop their one key. For instance, Odeg will only drop the Key of Destruction; never a Key of Hate or Terror. Prior to v1.08 Nekarat could only drop the Plan and was thus useless to any player who already had it, but in that patch he was given the ability to drop any of the three other keys as well.
- Monster Power 0: 5%
- Monster Power 1: 10%
- Monster Power 2: 20%
- Monster Power 3: 30%
- Monster Power 4: 40%
- Monster Power 5: 50%
- Monster Power 6: 60%
- Monster Power 7: 70%
- Monster Power 8: 80%
- Monster Power 9: 90%
- Monster Power 10: 100%
 Keywarden Visuals
|Key of Destruction||Key of Hate|
|Odeg in the Fields of Misery, Act 1||Sokahr in the Dahlgur Oasis, Act 2|
|Key of Terror||Infernal Machine Plan|
|Xah'Rith on the Stonefort, Act 3||Nekaret in Silver Spire, level 1, Act 4|
The Keys and Plan are Bind on Account so they can not be traded for. A character may have more than 1 of each key at a time, but each key is consumed by the crafting process, so you will need multiple copies of each key to build the multiple Infernal Machines required to explore each portal area and gather all the materials required to craft the Hellfire Ring.