|“||You puny humans think you can stop us? Us Mutants are unstoppable!||„|
Bigs is a member of the Toxic Mutants, an unnaturally born breed of beings made from noxious chemicals generated from humanity's pollution. They bear a hatred towards mankind, both for creating them and leaving them aloof as outcasts of society. As such, when Vrak arrives and offers him and Bluefur a chance to ally themselves with him, they promptly accept and, from then on, carry out the war against the Megaforce. By doing so, they indirectly become comrades to Malkor as well.
Bigs has, as all Toxic Mutants, lived isolated from humankind in the forests, lakes and mountains away from Harwood County. As he and Bluefur prepare to give the humans "a wake up call they can't ignore", they are greeted by Vrak and then joined forces with the Insectoids in order to complete their task more quickly. Bigs watches on as Bluefur summons a close friend of theirs, Hisser, and seeks them on the Mega Rangers. They are overpowered and all seems lost until a blinding sphere of light flies by Hisser and lands on the ground nearby, emerging as a mighty metallic warrior: Robo Knight. He introduces himself and takes on Hisser, easily outmatching and defeating him with his Robo Blade and Vulcan Cannon, from which he ultimately fires his Knight Dynamic and takes him down. Even when the Zombats turn Hisser into a giant, he simply converts himself into the Lion Mechazord and launches his Victory Strike, obliterating him, much to Bluefur's anger and Bigs' grief. Vrak is also upset, as he believes Hisser would have won if not for Robo Knight.
After yet another Toxic Mutant, Psychotick, is defeated by the newfound power of the Grand Strike, courtesy of the Gosei Grand Megazord, which Robo Knight acquire during his last battle against Vrak by combining himself with the Knight Brothers, the Sealion and Skylion Mechazords, Bigs calls upon Shadow Serpent to deal with the Rangers. After his first run with the Megaforce, which almost led the humans to their defeat, Vrak and Bluefur join Bigs and Shadow Serpent in a secluded conversation around the lake in which most of the Toxic Mutants live. They encourage him to defeat the Mega Rangers while Vrak advises him not to make the same mistake of underestimating them, as Creepox had done so in the recent past. Even with his superior strength, Vrak's concerns are highlighted when the Megaforce finally begins to work in unison and Robo Knight temporarily finishes him off with the Knight Dynamic. Upon seeing this, Malkor becomes enraged, as Vrak had not informed him of this plan and orders him to explain himself. Vrak simply sends his Zombats to enlarge Shadow Serpent. He overpowers both the Gosei Grand and Gosei Great Megazords but is defeated when they fuse into the newly-flush Gosei Great Grand Megazord and finally dispatched by its Double Strike.
As Distractor and his phantom army, consisting of Hisser, Psychotick, Skyfish, Gremlin, Kesaran and Mummy, fall before the power of the Ultra Mode, a powered-up state acquired due to the Wild Sword, an ancient artifact which Vrak also attempted to claim, Bigs and Bluefur tell Nojoke to follow Vrak's plan to the letter as to exploit human laughter and ensnare all those who laugh or even giggle into his gourd in order to dissolve them into oblivion. That, however, ends up in failure as Nojoke is dealt with by the full power of the Megaforce through the Ultra Strike and Knight Dynamic. He enlarges thanks to the Zombats and initially puts up a good fight by blowing fierce winds from his wings, even stronger than those of a hurricane, but the Sea Gosei Great Megazords soaks his wings and incapacitates this, allowing the Gosei Grand Megazord to use the Grand Strike and destroy him.
As Dream Snatcher comes along, Bigs and Bluefur use the Aurora Box, gained from Vrak, to increase his strength a hundredfold, which causes him to become capable of absorbing dreams of awakened people and to grow Roots of Despair which, if left unchecked, will rot the Earth to its core. Although he proves a challenge to the Megaforce and almost takes away one of their own, he is eventually defeated by the Ultra Sky Dynamic and then by the Gosei Great Grand Megazord's Double Strike. Tired of playing games with the Rangers, Bigs and Bluefur prepare to enact their master plan by infusing themselves with the power of the Aurora Box. They do so, and then set out to the city in order to begin the end of life on Earth.
The Megaforce fights with them, but is completely overpowered by the vastly superior strength and skill of their enemies. Even after the Ultra Mode is summoned, the Toxic Mutants are still able to retaliate with Bigs' newest special move: the Aurora Blast. However, they eventually pull through and blast Bigs apart with the Ultra Strike, instilling Bluefur to retreat. In the same night of that very day, Bluefur enlarges the Aurora Box and allows Bigs to assume his new form in unison with the royal weapon. As the Megaforce approaches to confront Bluefur, Bigs reveals himself anew and prompts Bluefur to battle the Mega Rangers, only for him to be stopped by Robo Knight.
As Robo Knight battles Bluefur, the Mega Rangers make their way into the Aurora Box and find Bigs hanging upside down from an organic network. He attempts to suck up their powers in order to increase his own, but it fails as the Mega Rangers break free from his toxic grip and eliminate Bigs from the inside, slaying him for good.
Bluefur becomes extremely infuriated. Vrak notices this and sends the Zombats to make him grow and avoid him to suffer them same fate as Bigs just had. Although he is successful in defeating the Gosei Grand Megazord, he meets his match when fighting the Command Ship, which the Rangers use to both destroy the Aurora Box and to engage Bluefur in battle. It transforms into the Gosei Ultimate Megazord soon thereafter. Despite being the strongest Toxic Mutant, Bluefur is unable to match the newfound strength of his enemies and is destroyed by the Ultimate Laser Cannon and Ultimate Strike techniques, putting an end to his kind and to the threat they posed to Earth.
Some time later, Bigs was reminded, along with Bluefur and Creepox, by Malkor when he conversed with Vrak about the recent defeats of their late allies and the need to complete the invasion before the alien Armada arrives.