Biri

The Biri is a volatile, electrical, jellyfish-like enemy that inhabits water-intensive or moist areas, with their most prominent appearance in Ocarina of Time within Lord Jabu Jabu's belly. In some games they are called Billy, a simple mistranslation that is canonically similar to the commonly  accepted name, Biri.

Characteristics
These foes, like their real world counterparts, exist primarily in aquatic areas such as Inside Jabu-Jabu's Belly in Ocarina of Time and the many dungeons of A Link to the Past, in small groups. While often light blue in color, in A Link to the Past, the Biri, exist in two forms: the red Biri is the stronger of the two, which splits into two miniature Biri when struck with the sword, the other being the natural blue hue common to other titles. Common to all incarnations is the method in which these foes can be defeated: these foes pulse with electricity, and sometimes experience lapses of non-electricity. During these non-electric gaps, Link must strike them with his sword, otherwise, they will simply shock him before he has any chance to strike. In Ocarina of Time, these foes can be defeated in a variety of ways including the use of the Boomerang, Deku Stick,  Bombs,  throwing Princess Ruto, or by use of the Deku Nut to stun before moving in with the sword.