As the heroes return to Earth, the Professor reveals a horrible secret about his past.
- Adaptational Villainy: Honeycutt is revealed to have sold the Heart of Darkness to the Kraang partly out of greed, whereas his past incarnations were always squeaky clean heroes. This sets him up to be The Atoner when he appears in the series.
- The Atoner: This is revealed to be Fugitoid's motivation, as he reveals that he was the one who built the BHG and was easily bribed by Kraang Sub-Prime to hand it over to the Kraang.
- The Bus Came Back: The supporting cast from the first three seasons make a comeback en masse now that the story has returned to Earth, and with both Dregg and the Triceratons defeated and out of the picture (along with presumably the Kraang, since the Technodrone destruction still took place, but offscreen), Shredder and the Foot Clan return to the Big Bad role.
- The Cameo: Kraang Sub-Prime returns in Honeycutt's flashback.
- Continuity Nod: Annihilation: Earth is revisited, revised, and undone by the end of the episode.
- Disney Death: Downplayed. The Shredder lunges for Splinter and the scene plays out so that it looks like Splinter has been killed once again - only for the camera to reveal that Splinter caught it and was merely reacting in surprise as opposed to suffering from Shredder's blow.
- Fugitoid is revealed to have survived his sacrifice right at the end.
- Earn Your Happy Ending: After seeing Splinter getting stabbed in front of them and a full season (six months in-universe) of trying, and failing, to steal the BHG before the Triceratons, the Turtles finally undo the ending of Annihilation Earth and can finally rest on their home planet.
- Et Tu, Brute?: Leo's reaction upon learning that the professor built the BHG, feeling as though the professor has been using them to steal it back. He quickly changes his tune when the professor sacrifices himself to destroy it. Notably, he doesn't bring up the fact that he sold it to the Kraang for money; he's only mad that he created the device.
- Fish out of Temporal Water: Though only by 6 months, the main cast are really the Future!Turtles, with everyone else from their timeline canonically Killed Off for Real. But they easily adopt the entire past timeline, Earth, and Past!Splinter as if it were their own, and let the Past!Turtles, that the timeline really belongs to, ship themselves off to space, never to be seen again.
- Fury-Fueled Foolishness: Leo's reaction to discovering that Professor Honeycutt was the one who created the Heart of Darkness in the first place is pure, unadulterated rage. Believing he's just using them to steal it back, he ends up embarking on a one-man assault on the entire Triceraton fleet, ignoring the others' pleas to stop and insistence that what he's doing is a Suicide Mission. Sure enough, during the assault, Leo's scout ship is blown up, leaving him stranded in space, his helmet is cracked, and he ends up passing out; the others retrieve him, manage to resuscitate him, and waste no time giving him a What the Hell, Hero?.
- Get A Hold Of Yourself Man: Raph to Mikey when the latter believes he's witnessed the deaths of their past selves.
- Heroic Sacrifice: The BHG can only be destroyed by a combination of dark matter and fusion. The Fugitoid is powered by a fusion core and his ship uses dark matter. It's pretty clear why he booted the Turtles off his ship when he did.Honeycutt: Let it be known, that you are my friends.... and I love you all.....
- I Hate Past Me: When our heroes voice how disappointed they are in his past actions, this is Professor Honeycutt's sentiment about his former human self, for being just greedy enough to build the Heart of Darkness for the Kraang.
- Karma Houdini Warranty: After seeing three seasons of the Shredder completely curb-stomping the turtles, pretty much everyone else, getting away with everything he does for the sake of his revenge, and killing Splinter out of selfishness, Shredder's streak comes to an end when a rip-roaring pissed Splinter gives him a long-overdue No-Holds-Barred Beatdown.
- Killed Off for Real: From the looks of it, the Triceraton Empire. Additionally, it's unknown if any Kraang outside of those commanded by the Primes survived the Triceratons' assault, but knowing Sub-Prime...
- This also confirms that going to the past created two sets of turtles, and everyone from the original timeline is in fact dead and gone. Stopping the annihilation didn't undo the damage, but saved a new universe that's an otherwise identical duplicate of the old one.
- Killed Offscreen: The destruction of the Kraang evidently still happened, but it is not shown this go round.
- Leeroy Jenkins: Leo loses his mind when Honeycutt reveals he created the Heart of Darkness and goes on a solo assault on the Triceratons that is outright called foolish by his friends.
- My Future Self and Me: The Turtles meet and fight alongside their past selves. The younger Fugitoid taking the younger Turtles on a space adventure for unexplained reasons fixes the problem of having two Turtle teams.
- Mythology Gag:
- Professor Honeycutt has previously sacrificed himself to save the Earth from the Triceratons in past incarnations.
- No-Holds-Barred Beatdown: Splinter is so pissed at Shredder for betraying their Enemy Mine against the Triceratons, on top of being willing to ensure Earth's destruction for the sake of his revenge that he beats him into the ground. The next time we see Shredder, the beating Splinter gave him has left him bedridden and in intensive care.
- Set Right What Once Went Wrong: Not only have the Turtles saved Earth from the BHG, but Splinter also survived Shredder's back stab and proceeds to wallop him for that.
- Taking You with Me: What the Fugitoid does with the Triceraton fleet.
- Villain: Exit, Stage Left: When Splinter defeats Shredder, Tigerclaw collects his wounded master and calls for the Foot to retreat to fight another day.
- Voodoo Shark: Just as everyone's wondering what to do with two sets of Turtles, plus two Aprils and Caseys, the past Fugitoid arrives and takes all the past selves off into space because reasons, even though they won't be going back in time again and don't need to recover the BHG anymore (though it's possible this Fugitoid is doing this to keep this new time loop stable).
- What the Hell, Hero?: The others rip into Leo after his suicidal mission against the Triceratons.
- Also, half of the Hamato kids (mainly Leo, Raph, and Casey) have this reaction to Honeycutt being the BHG's inventor.
- Wham Line: "You see, it was not the Kraang who invented the Black Hole Generator. It was... I who created it."
- You Monster!: Shredder claims he's trying to rid the world of a monster when he tries to kill Splinter - and Splinter retorts that he's the only monster.Shredder: I will rid the world of a vile monster!Splinter: The only monster here is you, Saki!
