Heatblast

"Heatblast is a classic." - Ben Tennyson.

Heatblast is the Omnitrix's DNA sample of a Pyronite from the planet-like star Pyros.

Ben as Heatblast
Heatblast has molten rocks across his body. As Ben has aged, Heatblast has gained two mini-volcanoes on both shoulders.

Ken as Heatblast
Ken as Heatblast looks similar to his appearance in Omniverse.

Credit
The picture in the infobox belongs to elmike9.