Kevin's Abilities | Ben 10

Kevin's abilities have somewhat changed through out the course of the series. Generally, his power revolves around absorption. In Ben 10, Kevin can absorb energy and manipulate machinery to a minor extent though the energy he uses is finite, so is required to steal more. By absorbing energy from the Omnitrix, Kevin can temporarily take on attributes of any alien form Ben has currently taken on.

In "Framed", it is revealed that Kevin is able to assume any of Ben's alien hero forms at will, due to having absorbed enough sufficient energy from the Omnitrix. Despite this advantage over Ben, he is still defeated. The rage causes his absorption power to spiral out of control, mutating him into a hulking behemoth fusion compromised of the ten starter Omnitrix aliens with no way to revert back to human form. He remains in this form for the remainder of Ben 10. According to the enhanced version of "Framed" Kevin's human DNA restores through time. So, after 5 years he will become a human again. 

 Kevin's stone form

In Ben 10: Alien Force (5 years after the Ben 10 series), Kevin returns in human form with his absorption powers intact. However now, he is able to absorb the properties of material into his own being such as metal or rock, transmuting himself a living form of whatever material he has absorbed and use it to increase his physical strength. It is revealed in the episode All That Glitters that the transmutation actually serves as a second skin/coating that eventually peels away as he takes damage. In the episode Plumbers' Helpers, Kevin can absorb multiple materials at once, as demonstrated by absorbing both nickel, copper and zinc (from loose change in his pocket). Dwayne McDuffie stated that Kevin can, in fact, still absorb energy, but is "afraid to", a plausible reason, considering his previous mutation. He requires a decent amount of material to completely encase himself. This abiltiy has once been used productively when Kevin was forced to synthise a coating of precious material, with the coating thickening after multiple absorbions to the point where Kevin couldn't move. 

 In the Alien Force season 3 premiere, Kevin loses the ability to revert to his human form after a feedback blast, caused when Ben tampers with the Omnitrix, imprints various materials onto him, such as concrete, metal, wood,;what appears to be Diamondhead crystals. in addition, Kevin gains limited shapeshifting abilites, seen when he shifts his hands into a variety different tools, such as a mace and large clippers. It is unknown if this is a permanent conditions, or simply temporary.