A fierce feline predator from Capella IV able to deliver a powerful electrical charge, one of which is held in the menagerie of Kukulkan's ship.
The Capellan power-cat is a large, bad-tempered predator native to Capella IV, seen in the animated episode How Sharper Than a Serpent's Tooth. The animal can throw off a strong electrical discharge, and according to McCoy none had ever been kept alive in captivity, since the species cannot bear confinement.
The winged serpent Kukulkan keeps one among the creatures in his shipboard zoo, where each specimen is held in a cage that feeds it the illusion of its home environment.
Kirk and McCoy break the cages open to distract their captor, and the enraged power-cat turns on Kukulkan. Kirk brings it down with a tranquilliser from the doctor's medical kit, saving the being who had been holding him prisoner.