Trinexx

Trinexx is the boss of Turtle Rock in A Link to the Past and the last dungeon in Ancient Stone Tablets. Its name may be derived from the prefix "tri-" meaning three, and the word "necks," alluding to its three heads. Its first form is a stone turtle with two additional heads protruding from its shell on either side. These extra heads are elemental - the red one spouts flame and the blue one breathes frost.

In order to defeat Trinexx one must use the Fire Rod on the blue head and the Ice Rod on the red head to stun them. One can then attack them with the sword to destroy them. Once one of its heads is gone, its main head will begin to reach out and lash at you. After both are gone, Trinexx will withdraw into itself and its shell will explode, revealing its true form as a giant snake with a glowing orb in the center of its body. In this form it attacks you directly with its body. Hitting the orb three times defeats this boss to win the dungeon's crystal and Heart Container.