Plot

Young Harley is having a dream birthday; he and his family are going to watch the taping of his favourite show. But the dream becomes a nightmare when the animatronic stars turn homicidal.

A boy named Harley and his family (brother Austin, mother Beth, and step-father Mitch) attends a taping of The Banana Splits TV show, which is supposed to be a fun-filled birthday for young Harley and business as usual for Rebecca, the producer of the series. But things take an unexpected turn -- and the body count quickly rises. Can Harley, his mom and their new pals safely escape?

A young boy named Harley is a huge fan of The Banana Splits. On his birthday, he, his parents Beth and Mitch, and his older half-brother Austin, go to a live taping of the The Banana Splits at Taft Studios. When they arrive, Harley waves at the characters - Fleegle, Bingo, Drooper, and Snorky - who were driving one of the Banana Buggies, almost getting himself hit. As the outing is getting ready, Andy, the Vice President of programming, informs the show's producer Rebecca that the show is being cancelled after the recording. After the taping, the characters (who are actually robots) learn about the cancellation of their show from their co-star Stevie, and begin a body count around the studio, starting with Drooper stuffing a lollipop prop into Stevie's throat.

Outside the studio, Beth learns that Mitch has been cheating on her, and he explains it's because she was always with Austin and Harley, and not him. As Mitch gets his car ready to go home, Snorky, who is driving the Banana Buggie, chases and runs over Mitch. Meanwhile, Thadd and Poppy, a couple, arrive in the Fleegle's Magic Shop set, and happily get engaged. However, Fleegle arrives and kills Thadd by sawing him in half, and when he attempts to do the same thing to Poppy, he hears Harley, along with his friend Zoe, trying to find Snorky. He takes them to the back room where the characters were made, and traps them with another girl named Parker.

Beth, Austin, Rebecca, and the show's host Paige, learn about the Banana Splits' carnage when Parker's father Jonathan comes completly injured (Drooper lit his face on fire), which makes Beth and Austin go out to look for Harley and Zoe, while Rebecca heals Jonathan and Paige goes to call 911. While looking for the kids, Austin and Beth come across Poppy, who is sobbing over Thadd's death, and convince her to join them on their search.

Meanwhile, Harley, Zoe, and Parker meet Karl, the man responsible for the creation of the Banana Splits, and beg him to let them out. He almost does so, but gets distracted when Drooper comes dragging Bingo (who was attacked by Beth when he tried to attack Austin), but the kids were able to get out and trap Karl in their cell and run off.

Meanwhile, Rebecca and Jonathan get captured by Fleegle and Drooper, who take them to one of the stages, "The Sloppy Time Course", and force them to complete it in order to escape. However, when they reach the end, Fleegle stabs Jonathan in the back with a key, while Drooper smashes Rebecca's head with a hammer. While trying to find the way out, Harley, Zoe and Parker come across Snorky. Harley tries to convince him to help them, to which Snorky agrees.

Beth, Austin, and Poppy find Paige, who informs them that she was unable to call the police because the phones aren't working and the cellphones were smashed. The group go to the Back Room to ask Karl how to stop the Banana Splits. He provides no information, but when the group hear music coming from a hatch, they go in as there may be danger in there. Just as she's about to follow them, Poppy noticed a mask for an unused fifth Banana Split named Hooty. She puts on the mask, and kills Karl as revenge for Thadd's murder.

Beth, Austin, and Paige are shocked to see that Fleegle and Drooper have been entertaining chained scared and crying children with violent and gruesome things, like burning Stevie's dead corpse, and ripping Andy's limbs off. Harley, Zoe, Parker, and Snorky arrive and get locked with the other kids. However, Snorky gives Harley the keys to the chains that are on the children's feet. He unlocks the chains, freeing the kids and they run to the exit. Beth attempts to attack Drooper and Fleegle, but gets overwhelmed, and almost dies when Austin and Harley arrive and help her kill Fleegle and Drooper.

Beth, Austin, and Harley run towards Paige and Zoe to reunite with each other, only to be cornered by Bingo. He declares "time's almost up", but then Snorky appears and has a fight with Bingo. Bingo outnumbers Snorky by taking his heart out. However, Snorky was able to crush and crack Bingo's head, killing him. Harley comforts Snorky, telling him he will always be his favorite, before Snorky dies.

In the aftermath, the police arrive, Austin and Paige develope romantic feelings towards each other, and Beth divorces Mitch (who survived his encounter with Snorky). Mitch gets left behind when the police leave, and ends up getting run over again by the Banana Buggie (this time killing him), now driven by Poppy and has the remains of the Banana Splits on the back. As Poppy is driving the Banana Buggie, Fleegle is seen reactivating, and then laughing.