Amps as they are seen in New Super Mario Bros..
The Amp is a rather odd enemy in the Mario series. He is a ball of electric energy who floats around in mid air. He has a face complete with eyes, and mouth, it is almost reminiscent of a clown face. He is about the size of a Goomba though his size can vary. He typically moves quickly in a circle pattern blocking where Mario has to go to progress. He also may move back and forth or just remain stationary. He can sometimes be hard to avoid and may take Mario`s health often when he is around. He can not be defeated by Mario in any way.
In Super Mario 64 for the Nintendo 64 and Super Mario 64 DS he is a rather common enemy encountered throughout the two games. In these games he tends to move in circles blocking Mario`s way, ether on platforms, narrow bridges, or paths. Mario will get electrocuted and lose some health if he runs into him.
In New Super Mario Bros. he is pretty rare and just stays in one spot only. Mario must than just go around him to avoid him, and if he runs into him he will lose health or lives. The Amp`s in this game also appear a little larger than the Wii New Super Mario Bros.
He now has appeared in his second 64 title Super Mario Galaxy 2, again in this game he is rather rarely encountered. He appears smaller in this game and moves back and forth on small platforms that Mario must jump onto. This makes him hard to avoid because of the small area in which he moves across.
 Mario Party Series
He also makes an appearance in some minigames in the Mario Party Series. During the minigames he appears in he must be avoided by the players, if a player runs into him or if he runs into the player they will lose the minigame.