All Up to You: When the rest of his brothers are escorted to the kid's room, it falls on Raph to get the information they need.
Bait-and-Switch: When Raph arrives in the kiddie room, Mikey yells “new toy!” like he did with Donnie and presumably Leo. However, since the librarian was there as well, Mikey sent the kids after her instead of Raph.
Evil Is Petty: Due to the turtles previously foiling their plans, the Foot Lieutenant and Brute decide to mess with their plans to find the book that will free Mayhem.
Hates Baths: Mayhem teleports himself into April's bathroom mirror to avoid having to take a bath, triggering the whole plot.
Here We Go Again!: After being freed from the mirror, Mayhem almost immediately teleports himself back in.
Inevitably Broken Rule: The obvious rule of the Mystic Library is to stay quiet. Mikey breaks this rule immediately.
Library Episode: It originally starts out in the New York City public library, but the turtles find their way into the titular mystic library.
Nice Job Breaking It, Hero: When April calls Raph, she yells at him loud enough to get the Hush-bats to start chasing him.
Offscreen Moment of Awesome: Despite being taken captive and forced to become a plaything to the yokai children, Mikey somehow takes over the kiddie room and has become their leader by the time Raph shows up.
Portal Door: Donnie finds a book, which transports him and his brothers to the mystic library.
Punch Catch: The Foot Brute does this with Raph. The fight stops there as they're under surveillance.
Race Against the Clock: The turtles have to hurry before Mayhem disappears from the mirror he's trapped in.
Rule of Three: The “new toy!” gag happen three times on screen. First when Mikey arrives, then Donnie, and finally Raph and the librarian.
Scary Librarian: The mystic librarian is a large bat yokai who has small bat minions that will take any noisy patron to the kiddie room. Later, when she catches Raph creating a lot of noise and destruction, she unfurls her wings and threatens to pummel him into papyrus.
Tickle Torture: The Lieutenant creates paper soldiers to tickle the turtles and to get them taken away by the Hush-bats. It works on Leo, but Raph blows another set back onto the Lieutenant, causing him to laugh and be taken away by the Hush-bats.
Ungrateful Bastard: When Raph frees him from the mirror, the first thing Mayhem does is scratch up his face.
The Purple Game
Aesop Amnesia: Right after defeating the giant robot, whose rampage was caused by his game, Donnie notices an ad for Purple game 2 and declares he must have it. His brothers are not amused.
Allegedly Free Game: The Purple Game offers players (cough, Donnie) the chance to spend real money for in-game points.
Cheat Code: Of the internal variety. Donnie enters a code in order to beat April.
Chekhov's Gun: Donnie uses the action figure that Leo got him to free himself from his restraints.
Forced to Watch: As part of their revenge scheme, the Purple Dragons restrain Donnie to his chair while they pilot the robot and make it attack his brothers.
Incredibly Lame Fun: The ad for the Purple Game looks cool, but the gameplay itself is pretty tame.
Nice Job Breaking It, Hero: By reaching rank 1, Donnie unleashes a giant robot on the city. Not only that, but it's controlled by his in-game avatar, making him directly responsible for the damage it causes.
Revenge: The game designers turn out to be the Purple Dragons whose sole purpose is to get back at Donnie for foiling their plans in “The Purple Jacket”.
Say My Name: When Donnie blows off his brothers again, Raph yells his name.
Shout-Out: Donnie and April’s in-game battle is reminiscent of Pokémon battles.
There Can Only Be One: Players of the Purple Game battle to reach rank one. The trope is even mentioned by name.
We Meet Again: Once the Purple Dragons reveal themselves to Donnie, Kendra greets him with the exact phrase.
Wham Shot: When Donnie’s new chair suddenly restrains his hands and feet, the Purple Dragon insignia lights up on the chair’s back.
