Season four of Teenage Mutant Ninja Turtles is split into two sub-sections that aired concurrently: thirteen episodes which aired daily in syndication, and twenty-six episodes that premiered in hour-long double-bills on Saturday Mornings on CBS, which would serve as its home for the remainder of the whole series. A brief "Turtle Tips" segment aired between the two episodes which served as PSA about the environment or other issues. There were a total of 20 "Turtle Tips" segments produced and aired. The syndication episodes featured the original title sequence, while the CBS episodes deubted a new title sequence, and also did away with the show's title cards. During this season, the Technodrome is back in Dimension X, having been launched through a portal at the conclusion of season three. The season premiere, "Plan 6 from Outer Space", aired in syndication, and detailed how the villains' battle fortress crash-landed on an asteroid; in the later episode, "The Dimension X Story" a volcano on the asteroid erupted, immobilizing the Technodrome by surrounding it with molten lava. "The Dimension X Story" was evidently intended to be the first episode of the CBS run, as many other episodes which aired before it from both the syndication and CBS episodes refer to the Technodrome being trapped in lava, but wound up airing very late in the season. Note that the Vacation in Europe episodes take place between the first two episodes of this season. Some episodes from this season were based off titles from other works. "Plan 6 from Outer Space" was from Plan 9 from Outer Space a 1956 film. "Four Turtles and a Baby" came from Three Men and a Baby a 1987 film. "Turtlemaniac" was from Listomania an intense fan frenzy. "Planet of the Turtles", was like Planet of the Apes but with other turtles. "Name That Toon" came from Name That Tune a game show from December 1952 to 1985 in September. "Turtles of the Jungle" had many reference to the King Kong film. "Menace Maestro, Please", Shredder dressed up like the Phantom of the Opera. "Super Hero for a Day" was from King for a Day. "Back to the Egg" was a title from a 70s song. "Slash: The Evil Turtle from Dimension X" is the eighty-third episode of the animated series Teenage Mutant Ninja Turtles (1987).
- Leonardo (Cam Clarke)
- Donatello (Barry Gordon)
- Michaelangelo (Townsend Coleman)
- Raphael (Rob Paulsen)
- Splinter (Peter Renaday)
- April O'Neil (Renae Jacobs)
- Shredder (James Avery)
- Krang (Pat Fraley)
- Bebop (Barry Gordon)
- Rocksteady (Cam Clarke)
- Slash (Pat Fraley)
- Donald J. Lofty (Rob Paulsen)
- Fenton Q. Hackenbrush (Peter Renaday)
- Con Donatello (Cam Clarke)
- Con Raphael (Barry Gordon)
- Channel 6 Newsvan
- Space Scowl
- Technodrome Space Vehicle
- Donald J. Lofty remarks that this episode is "not the first time" the Turtles have helped him, indicating that this episode takes place after one or both of this other appearances in "The Big Zipp Attack" and "Rebel Without a Fin".
- When Raphael and Leonardo grapple with Slash, Raphael is seen gaining Michelangelo's colours.
- Just before Slash smashes through the brick wall in the city, the con Raphael's beak is flesh coloured.
- When Donatello asks "What are they so miffed about?" before the angry mob chases the Turtles, Raphael is missing his pants.
- Leonardo's swords made a sheathing sound when Slash broke them.
- The markings on Donatello's shell where moved when he and Michaelangelo ejected from the Space Scowl.
- Donatello: We're gonna have to distract him so I can get to those controls!
- (suddenly a pizza box comes into Michaelangelo's view)
- Michaelangelo: April said he dug pizza! (he and Donatello kick Slash away into a pile of garbage where a steel bucket clamps onto his head)
- Michaelangelo: "Pizza time dude!!!"
- Slash: (pulling off bucket) "Give me that pizza!"
- Donatello: "Ohhhhh nooooo!!!" (he pulls the control lever sending the ship soaring skyward and Slash and Michaelangelo down a chute)
- Slash: "I want that pizza!!!!" (he takes the box aways from Michaelangelo and looks into it to find nothing there) What? No pizza? "You tricked me!!!" "EVERYBODY TRICKS ME!!!!"
Krang and Shredder are working on some super mutagen which they plan on using to create an army of super mutants that will take over the world. Bebop and Rocksteady decide to try the mutagen out on Bebop's pet turtle. The mutagen turns him into an evil Mutant Ninja Turtle, named Slash. When Slash starts destroying the place, Bebop and Rocksteady send him to Earth.
Fenton Q. Hackenbush (a developer for Donald J. Lofty) has a plan to do away with the sewer system and build condominiums. The Turtles find out what Fenton is planning and try to stop him. They phone April and make arrangements to meet and talk about Fenton's plans.
Meanwhile, Slash is looking for the palm tree from his water bowl on Earth, which is where Bebop and Rocksteady have told him it is. While looking for it, he meets Hackenbush. Hackenbush tricks him by saying he will show him where there are lots of palm trees if Slash will do something for him. Hackenbush tells him that he has to smash the Freedom Bell and everything else along his way. Hackenbush hopes that by having Slash do this, it will make the Turtles look guilty and get them arrested. This will get them out of the way so he can proceed with his plan for the sewers.
The Turtles find out from April that Slash is planning to smash the Freedom Bell. When they find him, they discover that they are no match for him. Even though he kicks their butt, they do manage to save the bell from being smashed.
Back in Dimension X, Krang and Shredder find out what Bebop and Rocksteady have done with the mutagen and are very angry. They send Bebop and Rocksteady to Earth to get Slash back.
Slash finds out that Hackenbush double crossed him and decides to get revenge on the city. He boards a rocket filled with garbage and threatens to crash into the city. The Turtles manage to steal the Techno Wing from Bebop and Rocksteady and use it to stop Slash from going through with his plan. Krang and Shredder open a portal for Slash's rocket to enter Dimension X, but Slash just flies by, dumping all the trash in the Technodrome.
After the Turtles tell Mr. Lofty what Hackenbush was planning to do, Mr. Lofty fires him and tells the Turtles not to worry about losing their home.