Lylirra made a blue post about drop chances. You have to have 5 stacks of Nephalim Valor and the drop chance scales up to 100% with monster power level.
You'll need five stacks of NV in order for the keys and the demonic organ pieces to drop.
Currently, both the keys and the demonic organ pieces (Vengeful Eye, Devil's Fang, and Writhing Spine) have higher chances to drop in higher MP levels, all the way up to 100% in MP10.
When they appear, they'll show us as legendary items, making them easy to distinguish from the other items the mobs may pop.
Diablofans posted information on the location of all of the keys:
- Key 1 - Found on Goat Mutant Key Warden in the Fields of Misery (Act 1)
- Key 2 - Found on Dune Dervish Key Warden in Dahlgur Oasis (Act 2)
- Key 3 - Found on Morlu Spellcaster Key Warden in Stonefort (Act 3)
- Infernal Machine Plan - Found on Terror Demon Key Warden in Silver Spire Lvl 1 (Act 4)
- The Key Wardens will always spawn in each Inferno game.
