Four Arms is a humanoid alien that is approximately twelve feet tall, has well developed muscles, two pairs of four-fingered arms, and red skin. A black stripe goes from his chin to his lower lip, and he has four eyes: a main pair, and a smaller pair below them.
In John Smith 10, Four Arms wears gold wrist and ankle bands, as well as two golden sashes that go across his chest. He appears as he did in the Ben 10-Generator Rex crossover, with black pants and fingerless gloves.
In Jane Smith 10, she wears a pink and black outfit similar to the Omniverse design, with pink eyes. The Omnitrix is on her belt. She doesn't have facial hair.
In Argit 10, he has an Omniverse appearance. The hair on the back of his head is spiked up, and his suit is orange and black.
For the Dimension 23 appearance, see below at Guts Man.
Four Arms was confirmed to appear due to the early introduction of the fusion alien Mummy Arms. He was unlocked in the episode Inspector Number 13 (Ryder 10). In his first appearance, Ryder was excited to use this form.
Guts Man is the version of Four Arms that is used in Dimension 23 by Megaman. He wears the blue Mega-Tech armor, the Omnitrix on his chest. His eyes are blue and his skin is a dark pink, similar to canon Handy Man. His lower left hand is replaced with the Mega Buster. He can't use the Buster for firing energy shots, but the force of the punch is increased by being made up of metal.