The Reptar Robot first appears in the Japanese Theme Park in Paris, France, EuroReptarland during the Reptar and the Princess Show rehearsal. However, during the rehearsal something goes wrong with the Reptar Robot and it's head breaks off, causing it to roll into the audience seats. After Reptar's head breaks off and crashes, Coco LaBouche gets angry and wants Stu Pickles to come to Paris to fix Reptar immediately. So Jean-Claude calls Kira and tells her to immediately call Stu, which she does. Kira calls Stu which makes him answer the phone (in the middle of the night) and Kira tells him the Reptar Robot he built has broken down and Coco wants him to come to come to Paris. When Stu realizes he's needed in France, he and Didi wake up in shock.
Later after arriving in Paris, and arriving in Reptarland, the Reptar Robot's head was seen in Coco's office. When the babies arrive in the office, Phil and Lil were shocked to see Reptar's head sitting there. Phil wonders if the Bobfather had anything to do with it. After Stu arrives in the office to see Coco, Coco gives Stu an angry look and angrily tells Stu she never wants to make this face again. She then orders Stu to immediately get to work. Stu promises Coco he'll have Reptar working in no time and quickly rushes out of the office to have Reptar fixed.
Later the next day, the Reptar Robot was seen in the Reptar Garage with another robot of Reptar's nemesis, Robosnail. Stu tells all the workers why don't they just follow his design and he uses paperclips and rubber bands for a reason. Stu then shows his family how Reptar works: when a person puts on the gear, whatever the person does, Reptar does. Stu puts on one of the gloves and waves his hand. When he waves, Reptar waves his hand. Stu then puts the helmet in Tommy's head. When Tommy nods his head, Reptar nods his, causing the man in Reptar's mouth to fall off but doesn't hit the floor cause of the cable that was tangled around his leg. Stu quickly takes the helmet off Tommy's head and apologizes to the man.
Later the next day when the Reptar Robot was fixed, the babies and their family were invited to see the Reptar and the Princess Show. That night, before going into the theater, Angelica tells Coco about Chuckie saying he wants the Princess to be his new mommy, and Coco's no Princess. This causes Coco to hatch a scheme. Later in the theater, when the show starts, the Reptar Robot at first starts rampaging through the village. But then the Princess appears and sings Reptar I Love You, a song that Reptar isn't a vicious dinosaur. Stu tells the rest of the family of how nice Reptar's head stays on during the show. However, during the show, Coco shows up backstage dressed as the Princess and drags her off the stage and she then appears singing the Reptar I Love You song. Chuckie gets out of his seat and walks up to the Princess/Coco and after she finishes the song, Coco grabs Chuckie's teddy bear, Wawa, out of his hands. Chuckie and the Princess/Coco then start fighting over Wawa as the show ends. The babies and Kira are shocked to notice Coco dressed as the Princess, but Chas claps for her believing she's talented and that he and Chuckie are both in love.
Later after Coco orders Jean-Claude to lock up the babies and Angelica, he takes them to the Reptar Garage where the Reptar Robot is kept when it's not in the show. However, indeterminate to stop Coco from marrying Chas, Tommy, Chuckie, Dil, Phil and Lil jump into the Reptar Robot while Angelica ties Jean-Claude's shoe laces to make him trip. The babies then start up Reptar and make him start to walk. After Jean-Claude trips cause of his laces tied together, the Reptar Robot breaks out of the Reptar Garage and starts walking through Reptarland. Angelica starts to give chase. Angelica gets onto a bridge, but Reptar then walks into it destroying it, causing Angelica to grab onto Reptar's nose. Tommy then pushes a button on the Reptar Robot's control panel, causing Reptar to shoot green stuff out of his nose causing Angelica to get covered in it and fall, but Chuckie causes Reptar to catch her into his hand. Angelica gets furious shouting this isn't the parade she wanted.
The Reptar Robot then passes by a daycare where is Kimi is. Chuckie then accidentally causes Reptar to break the daycare's roof off, scaring all the children, except Kimi, making them run in the process. Chuckie then makes Reptar lower his hand down and Kimi gets on. Reptar then walks through the Theme Park with Kimi and Angelica in his hands. The babies and Angelica then escape Reptarland, but as soon as the Reptar Robot starts going through the streets, Jean-Claude appears from behind them in Robosnail.
The Reptar Robot, controlled by Tommy and Chuckie, stomps through the streets of Paris, with Robosnail, controlled by Jean-Claude chasing after the babies. While chasing after them, Jean-Claude activates Robosnail's goo canons and Robosnail fires pink goo at Reptar. Reptar then steps onto one of the goo puddles and starts to slip. Reptar goes right through the Arc de Triomphe, but Robosnail is unable to keep going after him as he couldn't fit through it due to his snail shell. A police officer yells through his megaphone to try to get the babies to stop, but they couldn't. Reptar's foot hits a subway sign and goes flying into the air and lands on a fire truck, causing it to move forward with Reptar on it. The fire truck then moves down the streets with the Reptar Robot on it and heads towards a Seine. But Dil in his stroller, rolls backwards into a switch, activating the Reptar Robot's parachute. Reptar then gets pulled off the fire truck and it rolls and splashes into the Seine, but the Reptar Robot stops right in front of it.
While Jean-Claude in Robosnail kept going after the babies in Reptar, Jean-Claude calls Coco and warns her that the babies are on their way to the church, causing her to yell at him saying he disgusts her. The Reptar Robot then approaches the Eiffel Tower. Phil and Lil open a hatch to let Kimi and Angelica into the Reptar Robot's control room. But just before Angelica could climb into the control room, Jean-Claude in Robosnail grabs Reptar's tail causing Angelica to fall off the rope latter and grab onto one of Reptar's teeth and then Jean-Claude makes Robosnail swing Reptar with the babies inside him, and Angelica hanging on to one of his teeth, around and around in circles. Reptar's tail then breaks off causing Reptar with the babies and Angelica on him to get thrown upwards onto the Eiffel Tower and Robosnail with Jean-Claude in him to fall down. After Reptar hits the Eiffel Tower, Phil hits a red button, which activates the Reptar Robot's rocket booster. Reptar then gets rocketed upwards toward the top of the tower giving the babies and Angelica a wild ride. Reptar then hits the top of the tower and Angelica goes flying out of Reptar's mouth and up into the air. But Chuckie manages to get Reptar to catch Angelica before she could fall to her doom. Chuckie then finds the church from the top view of the tower, but makes Reptar let go when he finds at it. The Reptar Robot then starts to fall, but Chuckie causes Reptar to grab back onto the tower and Angelica falls again, but lands back into Reptar's mouth. Reptar then slides all the way back down to the bottom of the tower. Chuckie then gets the Reptar Robot to climb back down from the tower, but Chuckie then scratches his bottom thinking he's got a wedgie which causes the Reptar Robot to scratch it's bottom.
The Reptar Robot with the babies in it then approaches the church on a bridge, but Robosnail with Jean-Claude in him also goes onto the bridge. Reptar and Robosnail approach each other on the bridge and Chuckie knew he had to defeat Robosnail or else Coco was going to become his new mommy. As Chuckie makes Reptar get ready to fight Robosnail, Jean-Claude makes Robosnail charges towards Reptar. Reptar gets onto of Robosnail's shell but Chuckie makes Reptar's foot touch one of Robosnail's caterpillar wheels which causes it to break. Reptar then gets thrown off of Robosnail and Reptar lands losing his right arm (and Robosnail falls losing his right eye). Chuckie then makes Reptar grab Robosnail's other eye and stretches his left antenna like a rubber band, Reptar then let's go of Robosnail's antenna causing it to hit Robosnail making him spin out of control. Robosnail with Jean-Claude inside him then falls off the bridge and into the Seine. After Robosnail with Jean-Claude in him is defeated, Reptar with the babies in him then hurries to the church to save Chas from marrying Coco.
As Reptar approaches the church, Phil and Lil find the paperclips and rubber bands that Stu used to hold the Reptar Robot's head on. Not knowing this, Phil pulls off the paperclips and rubber bands and Reptar's head breaks off again. The Reptar Robot's head flies up into the air and crash lands onto the limo Coco rode to the church in, crushing and destroying it in the process. The hatch on the Reptar Robot's head then opens and an inflatable slide comes out, and Chuckie quickly takes off the glove and boots and slides out of the head and runs toward the church doors. Facing his fears of the golden dragon heads on the doors, Chuckie manages to get in and the babies and Angelica manage to stop Coco from marrying Chas. It's unknown what happened to the Reptar Robot afterwards.
The Reptar Robot is a Parody of Godzilla's Mechanical Doppelganger, Mechagodzilla, who debuted in the 1974 Japanese Toho Kaiju Godzilla film, "Godzilla vs. Mechagodzilla."