From the Super Mario Wiki
Li'l Sparkies are small sparks that travel along platforms, first appearing in Super Mario World. In later games, they seem to be almost completely replaced by Amps, an unlikely relative with similar traits and behavior. They are also similar to Sparks.
Super Mario series
Super Mario World
The Li'l Sparky (or Lil Sparky) makes its debut in Super Mario World. They have the same immunities as Boos (i.e. invincible to almost everything). Additionally, larger ones (referred to as Hotheads) can be found in #6 Wendy's Castle and Bowser's Castle.
Super Mario Advance 4: Super Mario Bros. 3
A Li'l Sparky is found in the E-Reader stage "Swinging Bars of Doom" and "A Sky-High Adventure" in Super Mario Advance 4: Super Mario Bros. 3. Unlike in Super Mario World, it can be defeated by Statue Mario's stomp or by Hammers thrown by Hammer Mario.
In Paper Mario, a Li'l Sparky named Watt was imprisoned and tortured by the Big Lantern Ghost. After Mario defeats the Lantern Ghost, Watt joins Mario's party, making her the first playable Li'l Sparky. Other members of her species may be contained in the lamps of the Lantern Ghost.
Mario and Luigi: Superstar Saga
Super Princess Peach
Notable Li'l Sparkies
Names in other languages