From the Super Mario Wiki
Amps, also known as Electro-Chomps in the New Super Mario Bros. Wii Strategy Guide or Zaps in Mario Party 6 and Mario Party 7, are small, electrified metal balls who have appeared as enemies throughout the Mario series. Their name stems from "ampere" (often shortened to "amp"), the standard unit of measurement for the speed of electrical currents.
 Super Mario series
 Super Mario 64/Super Mario 64 DS
Amps make their first appearance in Super Mario 64 and are featured in several levels through out Super Mario 64 and its remake Super Mario 64 DS. Similar to Li'l Sparkies and Hotheads, they move around objects and platforms and if Mario comes into contact with one, he will be shocked and lose one wedge of health. There is no possible way to defeat Amps in this game. Amps can be found in Bowser in the Dark World, Shifting Sand Land, Vanish Cap Under the Moat, Bowser in the Fire Sea, Tick Tock Clock, Rainbow Ride, and Bowser in the Sky. While being electrocuted, Mario will flash and become immobile for about one second.
 New Super Mario Bros.
Amps reappear as an uncommon enemy in New Super Mario Bros., in several Tower levels. In this game, they appear mostly in groups, and if Mario comes in contact with one, he will be shocked. They can only be defeated with a Mega Mushroom or Starman. They will lose their electricity for a moment if Mario or Luigi get shocked by one.
 Super Mario Galaxy
Amps can also be found in many areas of Super Mario Galaxy, including the Buoy Base Galaxy, the Battlerock Galaxy, and the Dreadnought Galaxy. They have faces, however their eyes and mouth are both bright red. There also other Amps that are large, face-less orbs, called Big Amps. Just like Super Mario 64, Amps cannot be defeated. They also appear in the Bubble Blast Galaxy. Here, they'll move on groups of two. The second player (if available) can manage to stop them, however.
 New Super Mario Bros. Wii
Amps also appear in New Super Mario Bros. Wii as rare enemies, behaving the same way they did in New Super Mario Bros. Only six of them appear in the first half of World 3 Tower. They can be defeated by freezing them with icy projectiles from the Ice Flower/Penguin Suit and then Ground Pounding them, touching them with a character using a Starman, or by having a frozen enemy thrown at them.
 Super Mario Galaxy 2
Amps reappear in Super Mario Galaxy 2, behaving the same way they did in the predecessor. Amps also have the same appearance as in Super Mario Galaxy. They can now be defeated by using a Rainbow Star. They appear in Sky Station Galaxy, Space Storm Galaxy, and Spin-Dig Galaxy.
 New Super Mario Bros. 2
Amps reappear in New Super Mario Bros. 2 for the Nintendo 3DS. They act just like they did in the predecessor and appear in levels World 4-B and World Flower-Cannon. Additionally, Amps can also be seen moving on lines, like Fuzzies.
 New Super Mario Bros. U
Amps and its giant variation reappear in New Super Mario Bros. U. They're acting like in the predecessor, also there is a new variation of amps interconnected with Bowser's face that conduct electricity each other.
 Mario Party series
They appear in various games in the Mario Party series.
Amps, still under the name of Zaps, appeared in Mario Party 6 as the Zap Orb. Once a player passed over a set Zap Orb, they would lose five coins for each space they moved beyond it for the rest of their turn. They're the only enemies in Circuit Maximus minigame.
Amps once again returned in Mario Party 7, still in the form of the Zap Orb, which had the same effect as before. However, the player lost three coins for every space instead of five.
A single Amp appeared in Mario Party Advance. There, it appears as a citizen of Town Area and needs help in winning a game in Town Game Room B. Notably, it sometimes uses electric terms in its speech. However, when the player enters the game room, Amp will tell him that he needs the player to help him break his losing streak. Once the player wins the minigame, Match 'Em, he or she will win the minigame. The end of the game states that he finally broke his streak on his own. They also appear in the minigames Amplifried, Cloud Climb and Broom Zoom as enemies.
 Appearance and Traits
Amps originally sported white "cross-popping" veins, joyful red eyes, and rounded metallic lips with a pure red mouth. Since Super Mario 64 DS and Mario Party 7, their appearance has been changed a bit. They now have more jagged yellow eyes and a larger, jagged mouth. Their lips are now white, with a pink tongue and black interior being visible inside the mouth. They are also now black rather than grayish and sport no angry veins.
 Names in Other Languages