Spark

Sparks are spherical electrical fires that move around the edges of blocks and walls, often in narrow maze-like areas. They originate from the Mario franchise, where they act essentially the same.

The Legend of Zelda: A Link to the Past
In The Legend of Zelda: A Link to the Past, Sparks flash between orange and blue and appear in dungeons starting with the Mountain Tower. They are completely invulnerable. A segmented enemy called the Firesnake acts similar and uses the same graphics, but stays orange.

The Legend of Zelda: Link's Awakening
In The Legend of Zelda: Link's Awakening, Sparks are much more common than before, first appearing in the first dungeon, the Tail Cave. They can be destroyed with the boomerang, which turns they into fairies.

The Legend of Zelda: Oracle of Seasons/Ages
In both The Legend of Zelda: Oracle of Seasons and The Legend of Zelda: Oracle of Ages, Sparks look and act as they do in Link's Awakening and are again highly common. They keep their boomerang weakness, which is easier to take advantage of in the former game due to the boomerang being an early required item rather than an optional secret like in Link's Awakening and the latter game.

The Legend of Zelda: The Minish Cap
In The Legend of Zelda: The Minish Cap, Sparks appear in dungeons starting with the Temple of Winds and additionally appear in a few caves. They retain their weakness to the boomerang, providing the same effect as before.