Ssserpent

Ssserpent is a villain in Ben 10: Alien Force. He referred himself as the "Snake that Walks Like a Man"(although he didn't have any feet to be able to walk). Serpent is voiced by Dee Bradley Baker.

Not much is known about his background except that he is half man, half cobra. He has snake venom like a normal snake does. He appears to be very slimy and have snake-headed hands. He so far appears to be one of Ben's weakest enemies, but apparently not for Gwen and Kevin. This ailen is similer to a Caricter(the giant talking snakes) in the secret saterdays.

Alien Force
Serpent first appeared in Vengeance of Vilgax: Part 1. He proved to be tough for even Gwen and Kevin only to be easily defeated by the arrival of Ben as Cannonbolt.

Ultimate Alien
He reappeared again in the Ben 10: Ultimate Alien episode Video Games as the secondary villain. Serpent says that he escaped from the Null Void Prison and he tries to fight Ben Tennyson only to be crushed by two cars that Fourarms used.

Trivia

 * Ssserpent so far is only defeated by two of Ben's original alien forms; Cannonbolt in Vengeance of Vilgax: Part 1 and Fourarms in Video Games.
 * It is confirmed by McDuffie that his name is Ssserpent.