Serrator is a Nighlok with six slitted eyes and a ricus grin. He can teleport, emit electricity, elongate his claw, and wields a weaponized Shaku in combat. In "The Tengen Gate," he was referred to as the Nighlok King (implying he once ruled the netherworld at one point). He was responsible for cursing Deker by turning him into a human/Nighlok hybrid and turning Dayu into a Nighlok as seen in "Broken Dreams" where his shadowed astral appearance appeared before Dayu's human form agreeing to save Deker's life in exchange for Dayu's humanity.
Serrator officially debuted in "Something Fishy" where he had been at the bottom of the Sanzu River and was revived by Master Xandred's recent power surge. He arrives aboard Master Xandred's ship to offer his services and revealing himself to be the one who sent Switchbeast. He shows off his heightened powers by obliterating an army of Moogers with a single blast and manages to convince a skeptical Master Xandred of his loyalty and asks for permission to enter the human world to scare enough humans to flood the river. Once on Earth, he introduces himself to the Rangers, and during their battle seems to have the Rangers beat, with all of the weapons they wielded unable to affect him. Serrator even cuts a piece of paper into a shape and creates Papyrox from it. In the nick of time, Antonio arrives and manages to use the Lightzord to successfully damage Serrator. Serrator then leaves commenting that the Rangers had "passed the test" for now.(oh, and the papyrox was destroyed)
In the episode "He Ain't Heavy Metal, He's My Brother," Octoroo criticizes Serrator for failing. Briefly after this, Serrator goes to attack the city again only to be met by the Rangers. He overpowers the Rangers again. Just as he is about to finish them off, Mia arrives only to be knocked down by Serrator. Jayden then passes Mia the Black Box allowing her to go into Super Samurai Mode. She manages to damage Serrator using her Super Airway Finisher. Before retreating, Serrator creates another Papyrox which is accompanied by some Giant Moogers and two Giant Spitfangs all of them being destroyed.
In the episode "Kevin's Choice," Serrator appears before Dayu to prevent here from disposing the half of Uramasa that was broken during Jayden and Deker's battle. Serrator then makes a deal with Dayu, offering to fix her Harmounium and Uramasa as long as she help him. It was revealed Serrator was the one who turned Deker into a half-human/half-Nighlok. He has Dayu send the message to Deker who Dayu had no idea was still alive. He instructs Dayu and Deker to crash the battle between the Rangers and Skarf and unleash Skarf's true power.
In "A Sticky Situation," Serrator catches up to Deker and Dayu as Deker asks about him fixing Uramasa. Serrator gives Dayu a special dagger and tells Deker that he will play a part in mankind's destruction.
In "Trust Me" serrator curses an island with fear ashes. when the rangers arrive he told them that the era of the sword will be replaced later having maldan and his master blasters. serrator,dayu and deker (the latter two who also attacked) retreat leaving a papyrox and 2 spitfangs to attack the rangers after the spell was broken. however all 3 are destroyed.
In "The Master Returns," Master Xandred learns of Serrator's secret plans and goes to Earth to deal with him. When Serrator is taking too long to get back to Dayu on repairing her Harmonium, she ends up confronting him which leads to an altercation where Serrator defeats Dayu. Luckily for Dayu, Master Xandred arrives and repairs Dayu's Harmonium upon reclaiming it from Serrator who flees. When Master Xandred is placed in the depths of the Sanzu River to recuperate, Serrator takes over his ship with no opposition.
Serrators plan is finally revealed in the episode "A Crack in The World" where Kevin notices how all his attacks form a straight line on the map. Serrator reveals during his next attack his true motives are to crack open the Earth so that the entire Sanzu River floods in, trapping Master Xandred in the Nether Worlds and heightening Serrators power to the point where he is equal to none. This will allow him to become the ruler of both worlds as well as create a new domain of his own.
To finally complete the spell starting in "A Crack in the World," he needed Deker to break the final point with his sword Uramasa. Serrator claimed that in doing so, Deker would also be free from his curse.
In "A Stroke of Fate," Serrator then plans to have Deker claim his prize in order for him to rip open the Earth. Serrator fights with Jayden, Mia, and Emily until Deker appears and Serrator gives Deker Uramasa in order to slash the barrier so that Deker can be free. Serrator is then betrayed by Deker at the last minute where he slashes Uramasa as Deker only worked with Serrator to get Uramasa fixed. Knowing his plans are ruined after the holes to the Netherworld close up, Serrator goes into an enraged fury before battling the Rangers once more. After taking a hit from the Bullzooka and the Cannon Strike attack, they defeat Serrator. Serrator then grows as the Rangers summon the Megazords. The Bull Megazord and the Light Megazord fights with Serrator while the Samurai Megazord and the Claw Armor Megazord to fight the two Papyrox. After the two Papyrox were destroyed by the Samurai Megazord and the Claw Armor Megazord, they help the Bull Megazord by combining the Zords into the Samurai Gigazord to fight Serrator and managed to strike him. The Gigazord uses the Shogun Strike on Serrator which he catches. Jayden then summons the Shark Zord which combines with the Samurai Gigazord. The Samurai Gigazord then uses the Ultimate Samurai Slash on Serrator. Before he succumbs to his injuries, Serrator states that he was supposed to split open their world not have it done to him.