A race of machine entities from the machine realm of Phyrexia. They are ruled by a godlike overlord called Yawgmoth, Father of Machines, aka The Ineffable. They are divided into castes such as Debasers, Plaguelords, Negators, Slayers, Gargantua, etc.
The Omniscientists of the old Sejannese Toral Pugnapax contacted the Phyrexians among other outsiders, but with the Phyrexians they made deals for the machines they could construct for them in exchange for magic items that they could not manufacture (having an aversion to the essence of magic). Soon, the Phyrexians made their move and invaded Crucibal destroying the Pugnapax and their capital of Iv Naresis was renamed Primus-One. They conquered the entire continent of Sejanna and had a treaty with the Hive Isles of Opticus.
They were banished back to Phyrexia by the power of the Staff of Law wielded by the Heroes of Crucibal during the White Flash.
There are rumors of their return, but no evidence has been found to corroborate this.