Biri are recurring enemies in The Legend of Zelda series.
A Link to the Past
Biri are first encountered within the Dark Palace. They do not make natural appearances, but rather, they appear after Link has defeated a Red Bari. If Link strikes the Red Bari with the Master Sword or a number of basic attacks, the Red Bari splits into two smaller Biris.
Biris have almost all the same attributes as their larger Bari counterparts. They resemble that of a floating jellyfish, with their bodies continuously bouncing around. They occasionally give off an electric shock, harming Link if he comes into contact. If Link comes into contact with a Biri, a full heart of damage will be done. If Link tries to slash at a Biri while it is electrified, again, a full heart of damage will be done.
Link can easily defeat these enemies from a distance using a number of projectile weapons. The Beam Blade from Link's Master Sword defeats a Biri with one shot. Alternatively, Link can get rid of these foes with the Hookshot.
Ocarina of Time
These floating jellyfish electrocute Link immediately upon contact. If they are defeated with the Sword, they also inflict damage to Link. To defeat them, Link must use Deku Nuts which then stun the jellyfish, allowing Link's Sword to cause damage either through a simple strike or a quick Spin Attack. Once Link has the Boomerang, he can use it to easily defeat them in a single hit. In general though, it is preferred to simply avoid them altogether.