Upchuck (voiced by Dave Wittenberg) is a Gourmand (from the French word meaning glutton) from the planet Peptos XI (Peptos being the Greek word for 'cooked' or 'digested'). Upchuck first appears in the episode "The Visitor", when an alien named Xylene enters a code into the Omnitrix, activating the form. He makes his first Ben 10: Alien Force appearance in the Season 2 finale with a new look to help fight the Highbreed.
Being a Gourmand, Upchuck has four strong, adhesive tongues that can stretch to great lengths, allowing Upchuck to latch onto large objects and reel them in with relative ease. Upchuck's mouth and stomach can also stretch, allowing him to swallow and digest objects fairly larger than itself. Upchuck possesses several acid-filled stomachs that dissolve almost all forms of matter, except ironically, ordinary human food and other organic matter. The items ingested are converted into explosive balls of liquids that can be expelled at will with great accuracy, he can also make them curve, like a boomerang, shuriken, or frisbee. This ability was demonstrated in Ben 10 Secret of the omnitrix. Upchuck also seems to be able to take a surprising amount of punishment for a creature of its size, able to take the brunt force of a moving car impact as well as surviving after being thrown through a wall.
In the Season 4 finale episode Upchuck was able to grab the sub-energy from the Forever King and swing him around. The Sub-Energy gave Upchuck super speed for that while. Afterwards Upchuck disperced it by firing the rest of the Sub-Energy into sky from Mount Rushmore. In the War of the Worlds episode of Alien Force, the new or "Teenage" version of Upchuck showed an ability of being able to fire blasts without ingesting anything.
This could imply that Upchuck has gained the ability to use the liquids in his stomach to belch up a blast at his opposer. We also saw that in the War of the Worlds episode that teenage Upchuck can not only ingest in-animate objects, but also projectiles being fired, such as lasers, etc. The new Upchuck also did not use the four adhesive tongues that he possesses or used to possess. this could mean two things, either he decided not to use them, or he lost them because they were only temporary for ten-year old Upchuck, as "Training Tongues."Upchuck can also keep swallowing and blasting a beam of energy as seen in "Vengence of Vilgax" when the escaped Chromastone keeps blasting the energy beam back to upchuck and he keeps swallowing it and regurgatating it back with no signs of injury.
Upchuck is unable to swallow ordinary human food. In the episode "Ben 4 Good Buddy", he remarks that he wasn't able to digest it. He is able to self destruct, probably after a continued amount of bad digestion. Upchuck also has a limit to how many big objects it can swallow. He is also slow when he eats a lot of things and becomes excessively fat, in his premiere episode "The Visitor" when he finishes eating the mecha-droid, he rolls around due to his fatness. Otherwise, he is somewhat quick, considering his small size, but due to his body structure his speed is limited.
Upchuck comes from the planet Peptos XI (Peptos 11). A once great planet that used to be filled with exotic wildlife. Peptos XI was the center of trade in the universe but after a while the food supply ran low so to adapt to the harsh conditions on their planet the gourmands learned to survive on what they could. After a few years they evolved harder than diamond teeth, four long adhesive tongues and four stretchy stomachs filled with super corrosive acid which can digest matter and fire it at will with great accuracy. Gourmands are literary eating machines, however they only eat inorganic food such as a car and because of that their only weakness is they cannot eat human food such as pizza because they cannot digest it.
In Alien force, Upchuck is able to spit balls of energy without digesting anything. He is now swampy green, lacks the suit, and the Omnitrix symbol is on his stomach instead of his left hand. His teeth are in better shape than before and he has Black spots on his back and sides.