Dead Matrix
From MediaWiki

The Dead Matrix is carried within the chest of Nemesis Prime.
Originally one of many Autobot Matrix of Leaderships from a mostly undocumented corner of the multiverse, it was corrupted over time inside of a defeated Prime. As the body lingered, eventually very little of Primus' essence remained inside. Using Nemesis Prime, Unicron's tortured clone of the fallen Prime, Unicron was able to insert a portion of his own dark essence into the artifact. This newly created weapon would be able to kill Primus should it ever be opened in his presence.

