“There comes a time when we all must grow up. When that time comes, it's important not to forget the lessons of our childhood. Because our childhood is the greatest training ground one will ever have.”
Once there, Lord Garmadon tells the Serpentine he is going to revive the extinct Grundal in another attempt to destroy the Ninja. As he is using the Mega Weapon, the Ninja watch and then burst in and interrupt the process.
Garmadon leaves in a hurry, while theSerpentine Generals steal a sarcophagus for compensation. The Ninja chase after them, but fall behind. The Generals can't fit the sarcophagus through a manhole with them so they left it behind and escape. The Ninja then realize they have been turned into kids. When the police arrive on the scene, they accuse the Ninja of the theft and take them back to the museum to apologize for their actions. The museum director accepts their apologies, but questions where the Grundal fossil has disappeared to. The Ninja realize the Grundal must have been revived after all, and to escape the cops, the Ninja disguise themselves and run off with some school kids that are on a field trip. The Grundal appears on top of the museum, scaring a crowd of people in the surrounding area.
Sensei Wu and Nya, worried that the Ninja haven't returned yet, leave Lloyd behind to go search for them. As Lloyd is playing a video game, he receives a call from Jay telling him to meet them at a pizza parlor and to bring their weapons. When they meet up, Kai informs Lloyd of the situation and the group wonders what they should do about the Grundal. Lloyd, knowing exactly who would be the most knowledgeable on the creature, brings them to a comic book store and introduces them to the sales clerk, Rufus Macallister. Rufus informs him that illuma-swords would work well, as the Grundal is nocturnal, but the shop only gives them out as a prize for winning a comic book trivia competition. Lloyd leaves a message for Sensei Wu and Nya back at the Destiny's Bounty, quickly telling them of what happened and their current location. Sensei Wu and Nya then go to Mystake for Tomorrow's Tea to turn the Ninja back into their older selves and the Grundal back into bones.
Meanwhile, Lloyd loses the competition (due to the final question being from a last-issue comic that had just sold out) and the Grundal shows up. The Ninja grab the illuma-swords to defend against the Grundal, but because they were meant as props they break easily. Lloyd attempts to take on the monster with his own powers but is quickly knocked aside. Just as the Grundal is about to consume the Ninja, Sensei Wu and Nya arrive with Tomorrow's Tea, tossing it to them and telling them to use it in order to age the creature back into bones, as well as themselves back into their normal states. The Ninja hesitate, realizing it would mean Lloyd growing older as well and missing out on his childhood. Lloyd, accepting the consequences, uses the tea to defeat the Grundal. The Ninja are returned to normal, but now Lloyd has become their age as well. The episode ends with Rufus handing Lloyd his last-issue comic, which he says he has earned. Lloyd declines, saying he already knows how it ends.
The final scene is a comic cover where Lloyd is defensively fighting against his father under a classic comic book font-stylized title of "Green Ninja."
When the Ninja are in the comic book store and preparing to fight the Grundal, Jay picks up Kai's suit instead of his own, but later, he is wearing his own suit.
Trivia
When Lloyd is walking into Buddy's Pizza, there is a TV in the upper left hand corner that is showing Cole, Jay, and Zane doing what they did before they joined Sensei Wu's team (Cole rock climbing, Jay testing out his homemade wings, and Zane meditating underwater in his home village), as shown in a flashback in The Golden Weapon.
Zane tells the others that "Nindroids don't dream," but "Never Trust a Snake" began with him having a dream about the Green Ninja. However, he may have been distinguishing between a dream and a vision. Normal dreams do not have significant meaning, but the "dream" in "Never Trust a Snake" revealed that the Green Ninja would have power of all four elements of Spinjitzu.
Zane is turned into a kid, despite the fact that he is a robot.
When the Ninja are kids, their Spinjitzu seems to be weak, which probably means that the strength of the Spinjitzu tornado depended on the user's age.
However, this is an exeption for young Lloyd, who is the strongest of the other Ninja, so it makes sense his Spinjitzu is stronger.
This episode uses the "regression" plot, where the adult main characters are regressed into kids.
