Appearance and Traits
Prototype Android take a very basic model, they are completely robotic in appearance and are a white in color (gray and brown as well in DBZ: Sagas). In Dragon Ball Z: Sagas, they nearly match the appearance of the Prototype Android seen in the image above, including the large extended head. In the game, they do not speak any words but make a strange synthesized robotic noise at times, usually after struck or when on the attack.
The Super Prototype Androids are much larger and considerably more difficult for the player to defeat. They have two chutes where their heads would be located, used for spawning the mini-androids. The mini-androids are very small, have a round body and only legs, and no arms or head. They are essentially walking bombs, and will flash red lights when close enough to explode.
Prototype Androids only make one appearance in the series, which is in a flashback that Future Trunks has about Dr. Gero, showcasing what his laboratory might look like. In his lab, strange robotic humanoids are seen on the wall, which are presumably Prototype Androids.
Video Game Appearances
They are heavily featured, however, in Dragon Ball Z: Sagas. In the game, Prototype Androids are antagonists that appear to battle the player just as the Saibamen do in the game. They are the main regular enemies during the chapter that tells Future Trunks' story. They also make an appearance in the early part of "The Androids" chapter that portrays the Android Saga, and are opponents when the player uses Goku (and Piccolo if there's a second player) to defend the Capsule Corporation building, and later with Vegeta while hunting down Android 20. All the prototype androids have some sort of jet pack on their backs enabling them to fly. Other than basic androids, there are also "Super" Prototype Androids, which are much larger and stronger than the basic ones. They spawn very small androids that are nothing more than walking bombs. These small androids will track the player and explode if close enough for a given amount of time.