Gibo

Gibos, previously known as Red Ghosts, are giant floating cell-like creatures made up of a transparent red membrane and a solid pink nucleus. The membrane is impenetrable to Link's weapons, and as such he must wait for the core to leave before attacking.

The Legend of Zelda: A Link to Past
In The Legend of Zelda: A Link to Past, Red Ghosts appear in Thieves' Town. They keep their nuclei within the membranes for a few moments before quickly emerging and floating a short distance, with the membrane then following. The membrane is completely invulnerable and only disappears once the core is defeated.

The Legend of Zelda: A Link Between Worlds
In The Legend of Zelda: A Link Between Worlds, Gibos appear in Turtle Rock. This time, the membrane moves before the core, and they additionally move much slower. The membrane can be destroyed by freezing it with the Ice Rod, leaving the nucleus defenseless if it is outside and defeating it instantly if inside.