From the Super Mario Wiki
Fizzlits are purple and tooth-shaped blob-like enemies found in Super Mario Galaxy 2. Mario (or Luigi) do not take damage from coming into contact with these enemies in their normal form. Instead, their sole mode of attack is flattening into an electric puddle that inflicts damage on Mario (or Luigi) if he touches this puddle. If Yoshi attempts to swallow the Fizzlit while it is in that form, Mario or Luigi takes damage, and Yoshi retreats inside his egg. They can be defeated by jumping on them, spinning into them, or eating them as Yoshi, all only while the Fizzlits are in their normal form.
Fizzlits appear mostly in industrial levels, such as in Bowser Jr.'s Fearsome Fleet, and in Bowser Jr.'s Boom Bunker. They also make a appearance in Cosmic Cove Galaxy.
These enemies reappear in Super Mario 3D World. Instead of having a tooth-like shape, they have a slightly taller, square-shaped body. Their electric puddle is also square, and can move from side to side. Unlike in Super Mario Galaxy 2, they cannot jump. In addition, the Fizzlits can make their electricity last a bit longer than normal when moving.
Names in other languages
||From "elettro", a prefix related to electronics, and "spalmare", to spread