The Turtles are hunted by a mutant turtle named Slash (who is actually Raph's pet tortoise, Spike), who has a personal vendetta against Raphael's brothers.
- Adaptational Badass: Slash. No longer is he the mutant turtle looking for his "Binky". Now, he's a mutated turtle with the body build of a luchador and a cunning to match.
- Aw, Look! They Really Do Love Each Other: All the turtles try to protect each other even though Raph was angry for much of the episode. Mikey and Raph want to find Donnie when he is missing (actually attacked by Slash.) Raph is horrified when he watches Slash attack Mikey. When they find Donnie, Raph is the one who sets Donnie's sprained arm. Donnie and Mikey still try to help Raph fight Slash even though they are both injured. Leo leaps into battle against Slash (not knowing that he used to be Spike) and at the end, Splinter reminds Raph that while he misses Spike, he still has his brothers. The closing shot is a group hug as Raph acknowledges that his brothers aren't so bad.
- Big Brother Instinct: Raph's love for his brothers is the reason why he went against Slash once his true desires are revealed.
- Arguably, the reason Leo actually stayed and had the tea party with the girl (who had threatened to scream if he didn't) instead of you know... just grabbing the mutagen from her and booking it.
- Book Ends: In the beginning Raphael runs in slow motion to save Spike while shouting his name. In the end, he does it again to save Slash from falling off a building. This time, he fails.
- Casting Gag: Corey Feldman the voice of Slash, previously played against Sean Astin, the voice of Raph, in The Goonies. Bonus points that Feldman played Donatello in Teenage Mutant Ninja Turtles (1990), so it's a return to the franchise as well.
- Cheerful Child: The little girl Leo has to have a tea party with. Not even having her bedroom destroyed by two mutant turtles or having "Mr. Turtle" run off with her new lamp that she was using to play tea party with managed to upset her.
- Chekhov's Skill: At one point, Splinter hits one of Raph's pressure points to calm him down for a bit. Raph uses this exact technique on Slash near the episode's end.
- Children Are Innocent: The little girl and her lack of fear is most likely a case of this.
- Continuity Nod: Slash is a mutant turtle from the original 1987 show and comics. However, this time, he's a mutated form of Raph's pet tortoise and his mutation was accidental.
- Create Your Own Villain: Spike (A.K.A. Slash) is after the turtles because he wants to "free" Raph from his brothers. It's because Raphael trained in front of him for years and vented his frustrations about his brothers to him. Furthermore, Raphael is the one who placed the mutagen canister in the same room as Spike then slammed the door so hard the canister broke open. It doesn't help that Raphael ultimately rejects Slash's offer of We Can Rule Together and calls Slash a freak.
- Dark Is Evil: Slash's bandanna color is black.
- Darker and Edgier: This episode manages to have the same dark tone "The Gauntlet" has. Unlike the other episodes, the turtles once again end up bruised, their shells scratched up, and Donnie with a broken arm.
- Divergent Character Evolution: Slash has numerous differences from his previous incarnations.
- Do Not Call Me "Paul": After mutating, Spike insists being called "Slash".
- Dramatic Unmask: Spike removes Donnie's and Mikey's masks when he beats them.
- The Dreaded Pretend Tea-Party: Leonardo's attempts to procure a vial of mutagen that winds up in the hands of a young girl is to attend her tea party.
- From Nobody to Nightmare: Spike, even though he heard Raphael talk about his brothers, had no real ability to do anything about them except nod his head and chew his leaf while sometimes watching Raphael train. After drinking Mutagen, now he's a frighteningly efficient combatant, can hit as hard he can run and uses stealth just like the brothers, and can overpower the Turtles in a straight fight. Slash isn't anyone's pet anymore.
- Imaginary Friend: Leonardo tries to convince the little girl he is having a party with that he is one.
- Instant Expert: Slash. He picks up on ninja skills pretty quickly. This is justified since he says that he had been watching the turtles train.
- Intellectual Animal: It is proven that Spike has always understood what others have said around him before he mutated. He reveals that he always listened to Raph vent his frustrations about his brothers and watched him practice. This is also foreshadowed in the opening when he glares at Mikey along with Raph, and smiles when Raph hits him.
- Lightning Bruiser: Slash is surprisingly fast, sneaky, and agile for a mutant turtle significantly larger than Raph and the others.
- Made of Iron: Slash is very durable.
- Mood Whiplash: In the second half, we go from Slash beating Raph up to Leo having a tea party with a little girl in her room.
- Before Slash's real motives are revealed, Michelangelo has a brief humorous moment where Slash's existence blows his mind. He then says that him and Raph need to look for Donnie, and when Raph accepts... Slash doesn't take it well. After this scene, Mikey's humor is almost entirely sidelined.
- Morality Pet: An inversion: Slash used to be Raphael's pet. Once he mutates, Spike's personality becomes MUCH more aggressive, which reminds Raphael that although his brothers may annoy him at times, they still are his family.
- Murder the Hypotenuse: A non-romantic example. Slash plans to kill Raph's brothers in order to "help" him.
- Mythology Gag: Slash's logo on his belt might be a nod to the belt buckles in the original TMNT cartoon. Also, the manner in which he learned ninjutsu (observing Raph train for years while still a pet) refers to the origin of the original Mirage Studios Splinter, who did the same with his own master.
- Nice Job Breaking It, Hero: Raph complaining about Mikey ruining his magazine, Leo sticking up for him and Donnie causing an explosion makes him so mad that he takes away Donnie's mutagen as an effort to keep Spike safe, which ends up spilling on the floor and mutating Spike.Donnie: Way to keep that mutagen safe, Raph.
- Recurring Extra: The old man that April duped twice in the first season returns. He actually doesn't run into any grievances this time.
- The pizza kid also shows up.
- Rule of Scary: They never explain how Slash is able to perfectly mimic Leonardo's voice and silhouette. The effect is still terrifying.
- Save the Villain: Even after everything Slash did, Raphael still tries to prevent him from falling off the rooftop.
- Shut Up, Hannibal!: Slash keeps telling Raphael that they aren't so different. Raphael doesn't take the comparison well after he witnesses Slash brutally attacking the other turtles.
- They Were Holding You Back: How Slash justifies his actions.
- Too Dumb to Live: The pizza delivery guy finds a mutagen canister in the street and assumes it's an energy drink. He's lucky Leo got it away from him.
- Unusually Uninteresting Sight: The little girl who ends up with the mutagen doesn't even flinch when a giant turtle kicks her tea cup into a wall.
- May be justified due to her, you know, being a little girl.
- Use Their Own Weapon Against Them: When Donnie tries to his Slash with his staff, Slash simply snatches it from him and uses it to knock him away.
- Visible Silence: Seen while Raph watches Mikey freak out about Slash/Spike.
- We Can Rule Together: Slash proposes that Raph work with him and leave his brothers.
- With Great Power Comes Great Insanity: Apparently Spike's mutation made him a bit crazy.
- Your Head Asplode: Mikey's head explodes when he meets Spike/Slash (not literally).
