Winder

Winders, also known as Moldola, are moving row of fireballs monsters appearing in several Zelda games. These creatures cannot be defeated. They look like several Sparks strung together.

Winders originally debuted in A Link to the Past. There they appear to be centipede-like monsters that move along the wall. They also appear in Four Swords and The Minish Cap acting the same way. In The Minish Cap, they can be found in the Temple of Droplets, the Palace of Winds, and Dark Hyrule Castle.

Known as Winder in Phantom Hourglass and Moldola in Spirit Tracks, these electrically charged monsters travel along walls, and so much as touching one can hurt Link.

These creatures are invincible in most games, so it is best to ignore them. However, in Spirit Tracks, they can be defeated by firing an arrow at the "head" of the creature (the largest ball of energy).

Trivia
Their appearance in A Link to the Past, Four Swords, and The Minish Cap is similar to the Moldorm from The Legend of Zelda. The similarity between the names, Moldorm and Moldola, should also be noted.