Necromentals
Necromentals are essentially undead elementals. An elemental that forms a bond with the Negative Energy Plane may become a necromental when it dies. Necromentals look like dark, dismal versions of their original being. For example, an earth necromental may look like it's made of grave dirt and dark stone, with tombstone pieces and the occasional bone jutting through.
Read more about this topic: Elemental (Dungeons & Dragons)