Kymellian density-power allows him to manipulate the spacing between molecules, expanding his body into an intangible cloud or condensing it into a high-density dollsize, and generating molecular density fields to protect himself and others from harm by solidifying air molecules, summon and displace his costume at will, enhanced healing powers which can be amplified even further by working with his siblings
Jack Power began his career as Mass Master in Power Pack (1st series) #1. He and his siblings later switched powers and he gained the gravity-power in #25, renaming himself Counterweight in #33. He assumed the energy-power in another power switch from #52, and took the name Destroyer in #54. Mass Master II was the Kymellian pseudoplasm duplicate of his brother, Alex.