At the outset of the original series, Ben had 10 forms he could access. Each of them has a name or nickname, although they are of a certain species. For example, he calls his Petrosapien form "Diamondhead," because of its crystalline appearance. When he turns into "Fourarms," the Tetramand, enemies beware of the extra butt-kicking power. "Ghostfreak" is the spooky Ectonurite form Ben can take. As "Grey Matter," the Galvan, Ben gets extra smarts, but can't do a lot of fighting. To crack the heat to full "Heatblast," Ben adopts his Pyronite self. When he changes into his Pisccis Volann alter-ego, he goes by "Ripjaws." Cover your nose when you see "Stinkfly" the Lepidopterran. When players could use an "Upgrade," Ben calls on the Galvanic Mechomorph's power. "Wildmutt" is the name of his Vulpimancer form. Finally, the extremely fast "XLR8" is a super-speedy Kinceleran.
During the course of the original series, Ben's powers grew as he unlocked new aliens whose forms he could take. These include: "Cannonbolt," the Arburian Pelarota; "Wildvine," a Florauna; "Upchuck," the alien Gourmand; "Ditto," of the Splixson; the To'kustar known as "Waybig;" "Eyeguy," an Opticoid; and "Eon," the Chronian. He also picks up the DNA for "Benmummy" a Thep Khufan, "Benwolf" a Loboan, and "Benvicktor" a Transylian.
Five years after the original series, Ben has to take on the mantle of the Omnitrix and defend the planet again in the Alien Force series. To that end, he has 10 new alien forms who help him in the task. "Swampfire" is a Methanosian fighter. "Humongousaur," is the massive Vaxasaurian. Calling out "Echo Echo" gives Ben the Sonorosian command over sound. "Jetray" swims through the air as any Aerophibian can. "Big Chill" is a Necrofriggian, giving him Ice powers. "Chromastone" is the energy-absorbing Crystalsapien member of Ben's team. Taking things literally, "Spidermonkey," is an Arachnichimp--using the root words Arachnid and Chimpanzee. The alien called "Goop" is a shapeshifting Polymorph. When Ben needs to "Brainstorm," who better than his Cerebrocrustacean alter-ego. Finally, "Alien X," a Celestialsapien, is almost godlike in his power, but must listen to three voices within.