This Seeking Tech guide will explain how you can get the missable Catoblepas summon in Final Fantasy V Pixel Remaster.
You can only find this enemy in Galuf’s World. Once you get there and acquire a submarine, head to the northwest continent on the map. From there, dive down and enter the cave.
Once you get out of the cave, run along the large forest area. This is where you can find Catoblepas as a rare encounter.
During the fight, the enemy will counter every attack with Demon Eye, which will turn your party member into stone. So make sure you heal after every counter attack before you attack the enemy again.
Once you beat him, the Catoblepas item will drop. Use it from the menu to acquire the summon.