Trantor needs children's souls he uses his victims fears. Among his treacherous kind followed a group of settlers from England to Briarville, in America and has been plaguing them for many years. In 1891, he almost captured all of five human children in his effort to use their life force to resurrect his people. Fornately he failed when he tried to take away a young girl who was used a bait for the men of Briarville to trapped him. The village elder, Phineas Worrell who lead the men to trap Trantor, put away the accursed troll by sealing him in the earthen soil under an oak tree in the woods. But Trantor was not finished: he made a prophecy that a direct descendant of Phineas' family would one day, release him from his earthly prison on the full moon night before Halloween, so that he would be free to complete his mission of bringing forth his offspring of trolls, thus unleashing a deadly army upon the world. In addition, he placed a curse on Phineas that his descendants would become dumber with each generation which would be proven useful to his advantage.
Role in the film
Fast-forwarding to the present day, Ernest is a sanitation engineer and he is ordered to clean up the land of the superstitious Old Lady Hackmore, who is actually the sister of one of Trantor's original four victims. However, when she learns that Ernest is a descendant of Phineas, she drives him away. Meanwhile, Ernest's middle school friends, Kenny Binder, Elizabeth, and Joey, are working on a haunted house, only to have it destroyed by Mayor Murdock's sons, Mike and Matt. Ernest suggests that they build a tree house so they have the high ground. After much searching, they discover a tree which Ernest deems perfect, unaware that it is the same one that feeds on the energy of Trantor's victims to grow pods which hatch into trolls upon touching the ground. After building the tree house, Old Lady Hackmore sees what Ernest has done and goes into a frenzy. It is then that Ernest learns of the legend of Trantor and that 'he' can release it. Skeptical, he performs the ritual for the kids (by touching the tree and saying "Yeah I call thee forth, Trantor!"), and inadvertently releases him. Scared stiff, the kids run off, leaving Ernest alone in the tree, where Trantor attacks him. At that moment, Ernest kicks over a cooler and milk spills out, causing Trantor to run off.
After running a distance, Kenny, Elizabeth, and Joey go off to their respective homes. On his way, Joey falls into a mudhole full of worms. Screaming for help, he feels his hand being grabbed. Hearing Ernest's voice, he thinks that it's him, only to look up and see Trantor, who transforms him into his first wooden doll (as punishment for bad acting) and places him in the tree, causing the pods to start sprouting. Ernest attempts to tell about his encounter to Cliff Binder, the sheriff, but he doesn't believe him, so he goes to Old Lady Hackmore. After consulting the legend of Trantor from the book "Trolls and Tree Devils", it is learned that the only thing that can stop Trantor for good is "the heart of a child and a mother's care". Being the descendant of Phineas, it's up to Ernest to save the town. He attempts to mount a defense against Trantor, but the townspeople do not believe his story and refuse to provide assistance (except for Chuck and Bobby Tulip, who take advantage of him by selling him phony troll weapons). Meanwhile, Kenny and Elizabeth return to the tree house, looking for Joey. There, they discover him as a wooden doll and see the pods. At that same moment, Trantor returns and see them. Hearing him coming, Kenny and Elizabeth run to Old Lady Hackmore's, with him following. Just as he's about to get them, he sees a boy on a skateboard.
Deciding to get Kenny and Elizabeth later, Trantor abducts the boy and carries him to the tree house, turning him into his second wooden doll (as punishment for bad acting). He is one step closer to releasing his army. The town doesn't believe Ernest and they care more about the Halloween bash more than the children. Ernest and Kenny form a troll-fighting squad and set up traps around the neighborhood. While at home, Elizabeth tries to make her mother believe what Ernest is saying is true, but she doesn't believe it. Hearing something under her bed, Elizabeth looks and only finds her stuffed bear. However, when she turns around, she sees Trantor sitting by her. He has claimed his third victim (as punishment for bad acting). Spotting Ernest at a store, Trantor decides to take a second chance at killing him. Jimmy, the cashier, sees him and tries to alert Ernest, but he speaks in gibberish. When Jimmy pulls out a gun, Ernest throws the milk he was holding in Trantor's direction, causing him to flee once again. Kenny soon meets up with one of his friends when he hears Elizabeth's voice coming from a pipe. Investigating it, he doesn't see anything, but when he turns around, he sees Trantor turn his friend, Gregg (who is dressed as a Native American) into his fourth wooden doll, (as punishment for bad acting) with plans to make Kenny the fifth one.
Trantor chases Kenny but vanishes when the milk truck drives between him and Kenny. Meanwhile, the parents go to Cliff, but he thinks the children are at the bash. Kenny then tries to tell him what he saw, but he won't listen. Ernest then shows up saying he caught Trantor, only when he opens the truck, it is revealed he caught Mike and Matt. Enraged, Mayor Murdock fires him. Kenny tries to back up his story, but Cliff takes him away to the bash. Ernest is about to throw in the towel but is reinspired by Rimshot, his pet dog, to keep up the fight. Trantor takes his two latest victims to the tree so their souls can feed his pods. He only needs one more to unleash his army. Ernest and Rimshot come there and see the pods, deciding to tell Old Lady Hackmore, only to have Trantor attack them on Ernest's pickup truck. After escaping him, Ernest looks over the legend of him and sees that trolls can be destroyed with something called M-I- -K. The audience knows that it means milk ("a mother's care"), but Ernest thinks that the answer is Bulgarian miak.
Knowing that Trantor needs one more victim, Old Lady Hackmore deduces that he will head to where the children are: the bash, which he does. Upon arriving there, Ernest rushes in to warn everyone about Trantor. Old Lady Hackmore is about to follow him when she sees a little girl fighting with her mother then make up, making her realize that unconditional love ("the heart of a child") is the key to defeating Trantor. During the costume contest, Matt Murdock picks a fight with Trantor, resulting in him turning him into his fifth and final wooden doll (as punishment for bad acting). Ernest attempts to destroy him with miak, but it doesn't work and he ends up getting thrown into the ice cream machine. Rimshot tries to help, but Trantor transforms him into a wooden dog. Trantor is about to destroy Ernest when he sees him covered in ice cream and flees.
Seeing what Trantor had done to Rimshot, Ernest is then determined to take him down. The townspeople, led by Mayor Murdock, decide to go to the tree house and stop him. At the same time, Kenny realizes that he can be destroyed by being exposed to milk, and rallies together a group of the local children, including Mike Murdock. Trantor reaches the tree first and places his final wooden doll into it, allowing him to free his army. As he laughs madly over his success at last, an enraged Ernest arrives and rams him with his truck, only for him to manage to escape. Ernest then sees that the pods are larger than before. They begin falling off the tree. He attempts to keep them from hitting the ground, but fails and Trantor's army literally rises. Meanwhile, Kenny and his troop obtain milk and squirt guns from the convenience store, much to Jimmy's anger due to them riding their bikes inside, and head to the tree house.
The townspeople arrive and are instantly overtaken by numerous trolls. Trantor orders his army to bring him Ernest's head. At that moment, Kenny arrives and spritzes the trolls attacking Cliff with milk, vaporizing them. Following his lead, the rest of the children begin doing so just as Ernest is about to be decapitated. Mounting their attack from the tree house, Ernest and Kenny soon take down the entire army. Everyone thinks that they have won, but Old Lady Hackmore appears during the cheering saying that it's not over yet. At that moment, Trantor appears. During the battle, he had called upon dark spirits to strengthen him, making him more repulsive than ever. Knocking Ernest out of the tree, he corners Kenny, who immediately sprays him, but he has grown so strong that he is immune to milk, and transforms Kenny into a wooden doll (as punishment for bad acting), making him even stronger. Jumping out of the tree, he faces off Ernest in their final battle, trapping everyone else behind a wall of fire.
Ernest initially attempts to fight Trantor with milk, but he hears Old Lady Hackmore say that only unconditional love can stop him. Ernest embraces him and begins dancing, overwhelming him with love and affection, finishing with a kiss (he and everybody were disgusted) causing him to explode. With him destroyed, his spell is broken and all the wooden dolls revert to normal since their punishment is over, including his original four victims from the 19th century which Old Lady Hackmore had watched over since his imprisonment. As Ernest watches everyone being reunited with their loved ones, he feels that there is nothing for him, until he sees that Rimshot has also returned to normal.