Pirantishead was the first monster that Lord Zeddcreated on Earth.
Made out of a piranha in Rampoon River, Pirantishead soon attacked Angel Grove, blasting skyscrapers to bits with energy rays from his Fish Horns. So powerful was Pirantishead that the Rangers summoned the Dino Zords immediately, before the aquatic creature had even grown. Unfortunately, Pirantishead blasted four of the Zords with his Fish Horns, freezing them solid. He quickly blasted the Tyrannosaurus DinoZord, and assumed command of the Zord.
When the DragonZord was summoned to protect the Rangers from the Tyrannosaurus, Pirantishead gained control of the Green Ranger's Zord as well. The Rangers retreated and tried to come up with a way to regain their Zords, in order to gain new Thunder Zords capable of combating Pirantishead. As Billy and Trini worked on a solution, the other four Rangers returned to combat Pirantishead. Unfortunately, the Rangers couldn't get near him, as he stood behind the DragonZord and Tyrannosaurus, who nearly destroyed their former masters.
Billy and Trini arrived with a signal blocker that could free the Zords of Pirantishead's command, but when something went wrong with the device, the others bought some time by blasting Pirantishead with the Power Blaster, sizzling the monster's feet. Eventually, the Rangers gained their new Thunder Zords, causing Lord Zedd to enlarge Pirantishead, who faced the Thunder MegaZord in battle. Unable to assume command of the Thunder Zords, Pirantishead perished by the finishing attack of the MegaZord's Thunder Saber.
Later on, Pirantishead was revived by Lord Zedd when he sent his best underwater monsters to destroy the Power Rangers. Pirantishead was nowhere near as powerful as he was before, and was destroyed by a supercharged slash from Saba.