Greensleeves (Experiment 342) is a green bear-like experiment with short fuzzy ears perched on his head, along with two antennae, white patches on his belly, around his eyes, and on the inside of his head, a light green shield-shaped marking on his forehead and a darker green sword-like marking on his chest.
To turn things back to the way they were in the Middle Ages. An extra set of attractable arms.
He isn't very strong. Instead he was designed to do his work under the protection of several other experiments. He also can't climb.
Jumba was inspired to create her after looking through and earth book about King Arthur. Hence his powers change things back to the way they were in story middle ages which can be different then actual historical middle ages. This also explains why he doesn't quite fit in with the other 300 series (Psychological), as Jumba created him on a whim. By turning things back to the way they were in the Middle Ages, he makes places easier to conquer or destroy.
Jumba unintentionally programmed Greensleeves to be a male. So he is rather polite and gentle, though he does have a small mischievous streak in his. He uses his power not out of an evil intent, but out of a genuine belief that people will be happier that way. It was because of the 'flaws' and because she tried to change some of his scientific equipment that Jumba dehydrated him soon after he was created.