While Monster Power is not required, each level will increase the drop rate of both the keys and the plans by 10%, all the way up to a guaranteed 100% drop chance at Monster Power 10. Players will be able to encounter the Keywardens in any difficulty, but only in Inferno and with a full five stacks of Nephalem Valor will they have a chance to drop pieces of the Infernal Machine. (Each component will be considered 'Bind on Account,' which means they can be used by any character on your Diablo III license.)

The Blacksmithing Plans will drop from Nekarat the Keywarden in Act IV - Silver Spire Level 1*.

The Key of Terror will drop from Xah'Rith the Keywarden in Act III - Stonefort.

The Key of Hate will drop from Sokahr the Keywarden in Act II - Dahlgur Oasis.

The Key of Destruction will drop from Odeg the Keywarden in Act I - Fields of Misery.

To craft the Infernal Machine, players will first need to collect four components from powerful Keywardens in each Act of Inferno:

Read on to find out how to craft the Infernal Machine, where it can be used, and what epic rewards await those brave enough to unlock its secrets. While the rewards for defeating these extra-bad bosses will be great, some assembly is required.

Ready for a double dose of diabolical danger? In patch 1.0.5, level 60 players will be able to forge a cursed construct called the Infernal Machine, allowing them to battle 'uber' versions of some of the most malevolent mischief-makers this side of New Tristram… in pairs.

Diablo 3 infernal machine key locations