Lil Sparky

Li'l Sparkies, also called Sparkies, are little sparks that travel along platforms, first appearing in Super Mario World. They usually behave similarly to Sparks.

Super Mario World
Li'l Sparkies (parsed Lil Sparky in-game) first appear in Super Mario World. They quickly move around platforms and are immune to everything but Invincible Mario. They are found in #6 Wendy's Castle and Front Door, specifically in rooms with Hotheads.

Super Mario Advance 4: Super Mario Bros. 3
In Super Mario Advance 4: Super Mario Bros. 3, Lil Sparkies are found in the World-e levels Swinging Bars of Doom, A Sky-High Adventure, and Puzzling Pipe Maze. Unlike in Super Mario World, they can be defeated by Statue Mario's stomp or by hammers thrown by Hammer Mario.

Paper Mario
In Paper Mario, a Li'l Sparky named Watt was imprisoned and tortured by the Big Lantern Ghost. After Mario defeats the Big Lantern Ghost, Watt joins Mario's party, making her the first playable Li'l Sparky.

Mario & Luigi: Superstar Saga / Mario & Luigi: Superstar Saga + Bowser's Minions
In Mario & Luigi: Superstar Saga and Mario & Luigi: Superstar Saga + Bowser's Minions, Li'l Sparkies make a cameo in three pseudo-sidescrolling levels to reach a Presenter. If Mario or Luigi is attacked by them, he will get knocked back to the beginning. They exhibit several different patterns in this game, including bouncing and floating like Amps.

Super Princess Peach
Li'l Sparkies (parsed Lil' Sparky) reappear in Super Princess Peach. They are behave similarly to how they act in Super Mario World, and are invincible to everything Peach can do. They are found in Shriek Mansion and Bowser's Villa. Unlike most other enemies in the game, they do not have a vibe-based counterpart.