Zol

Zol is the name of a gelatinous creature that shambles around its territory waiting for prey to come near. When hit, it may divide into Gel.

The Zol may have been the precursor to the ChuChus, seen in more recent Zelda games. Phantom Hourglass marked the first occasion in which both enemies appeared in the same game.

The Legend of Zelda
Zol are found exclusively within dungeons of the original Legend of Zelda. They are either black or gray in appearance and just crawl aimlessly around the dungeon, waiting for prey to come near. These jelly-like monsters have twice the offensive power as the smaller gel counterparts. Zol can be defeated with nearly any weapon in the game. If Link attacks a Zol using the Wooden Sword it will split into two gels. However, when Link gets the White Sword, the Zol will be defeated without even splitting into gels.

A Link to the Past
It appeared in A Link to the Past, found again in only dungeons and caves. They would come from ground after Link would walk over them. They lost their ability to turn to Gels. They come in 3 colors: red, green and yellow.

Link's Awakening / Oracle Series
In Link's Awakening the Zol returned, although it was not limited to just dungeons. Zol are native creatures to Koholint Island. They are now found in almost any habitat. It also had a new attack. Some would pop out of the ground to attack enemies, giving them somewhat of an Artificial Intelligence. They also came in two colors. The Red Zol, who didn't pop out of the ground, would divide into two small Red Gel after being hit (although an upgraded sword could kill it without it dividing), and a Green Zol, which popped out of the ground and could be destroyed in one hit with almost any conventional weapon. This species of Zol didn't divide when killed.

A similar type of Zol can be found in Oracle of Seasons and Oracle of Ages.

Phantom Hourglass
In Phantom Hourglass, the Zol returned, and retained its ability to split into Gels. This version can attach to Link, slowing him down and forcing the player to repeatedly rub them with the stylus to remove them.

Trivia
Zol is actually Loz spelt backwards, refering to Legend Of Zelda.