See Teenage Mutant Ninja Turtles for the entire franchise.
Ergo, the "red sky" seasons exist in a branched-off dimension that's similar, yet completely separate, from the rest of the 1987 dimension.
However, the "blue sky" universe—the 1987 dimension seen in Turtles Forever—still continued on separately. The last episode of the original show's seventh season (the last "blue sky" episode) establishes that the Technodrome gets sucked back into Dimension X, stranding Shredder, Krang, et al. on Earth. At some point, Shredder and Krang somehow retrieve the Technodrome and wreak havoc upon New York once again, and the Turtles intervene, thus leading to the events that get them stuck in the 2003 universe. The only forseeable problem is, Shredder and Krang return from that adventure with a drastically upgraded Technodrome, care of Ch'rell's modifications.
- Alternately, Turtles Forever happened in one of the earlier seasons of the 1987 show. There was no mention of those turtles being at the end of their adventures, and when we saw the city streets, it was still the '80s. The Technodrome snapped back to its original state and the show continued on the path we saw in elementary school.
- It'd have to be one hell of a Snap Back, though. It was shown that Technodrome 2.0 could travel to different dimensions without changing in form. Not to mention that it would take quite a bit of manual labor to downgrade it, and even Krang wouldn't be stupid enough to downgrade a flying Technodrome with a giant Death Ray. On another note, if you recall, the special didn't say anything about any of the Turtles seeing an end to their adventures—for instance, Karai insists that Ch'rell will return, and Hun is still a giant mutant turtle, so the 2K3 Turtles will have plenty to do upon their arrival home (even if the viewing audience never gets to see it). The same could be said for the 1987 Turtles, who now have to deal with Technodrome 2.0.
- Don't worry about the Upgraded Technodrome, Bebop and Rocksteady will continue to wreak the 1987 Shredder and Krang's plans, no matter how sophisticated the new technology is, those two will do something stupid. And the 1987 Turtles will eventually find a way to fight the new ninja bots.
- It'd have to be one hell of a Snap Back, though. It was shown that Technodrome 2.0 could travel to different dimensions without changing in form. Not to mention that it would take quite a bit of manual labor to downgrade it, and even Krang wouldn't be stupid enough to downgrade a flying Technodrome with a giant Death Ray. On another note, if you recall, the special didn't say anything about any of the Turtles seeing an end to their adventures—for instance, Karai insists that Ch'rell will return, and Hun is still a giant mutant turtle, so the 2K3 Turtles will have plenty to do upon their arrival home (even if the viewing audience never gets to see it). The same could be said for the 1987 Turtles, who now have to deal with Technodrome 2.0.
- Most likely, sometime after the last episode of the 1987 show and before Turtles Forever, Shredder and Krang were able to have the Technodrome rebuilt with help from Krang's followers and slaves. They are now back on Earth, but the Turtles stopped them from bringing Krang's army to Earth. So now they're back to the way things were in the old days until they ended up in the 2003 universe.
- An interesting theory...how are we to know what would happen if a being gets killed in a dimension not its own?
- Alternatively, maybe Ch'rell had a transdimensional fail-safe built into his robot suit in case of an extreme emergency. 1987 Don proves that a tote-bag sized transdimensional transporter is possible, and we never see the Utrom itself get vaporized, so perhaps Ch'rell got beamed to another dimension as a means of escape.
- Alternatively, Ch'rell might've been sent to the universe of the 2012 TMNT series being made for Nickelodeon, and the 2012 TMNT will have to team up with the 1984, 1987 & 2003 TMNT to stop him.
- This troper thought the same thing. However, characters from the other continuities won't make an appearance since the 2012 cartoon will likely be self-contained from the multiverse. Ch'rell will exist as a spirit taking the form of his Shredder armor, and influence the Shredder of the new cartoon. It won't be revealed that its Ch'rell, but it'll be obvious.
- Kind of Jossed. It has already showed that the 2012 Turtles shares a multiverse with the same of the others, or at least with the 1987 one. There is still a chance that Ch'rell would make an appearance as himself and the turtles would have to team up to defeat him.
- This troper thought the same thing. However, characters from the other continuities won't make an appearance since the 2012 cartoon will likely be self-contained from the multiverse. Ch'rell will exist as a spirit taking the form of his Shredder armor, and influence the Shredder of the new cartoon. It won't be revealed that its Ch'rell, but it'll be obvious.
For I.E.: The 2000s Turtles are from universe in which Cyber-Shredder never happen—but they did get trapped in the Future—mostly like dealing with an alien version of Shredder and Cody's evil uncle. They return to their own time without Cody's robot following them. The 1980s Turtles are from a universe in which Technodrome just got it's tank wheels removed and stuck in a small Forrest in New York. Likely, it was a easy repair job for Krang, Shredder, Bebop and Rocksteady-allowing the Technodrome to move into New York to do stuff-leading to Shredder's ooze robbery and the explosion that lead to the crossover.
- Except their Cyber Space technology is referenced in the movie suggesting Cyber Shredder did happen.
- The Technodrome computer did make note of a "temporal anomaly", which could indicate that some form of time travel came into play. Or maybe the '87-verse and the '03-verse have their time streams synched in some kind of significant way, even though both series technically should (and do) take place decades apart.
- They're synched by the Turtles. After all, they're the keystones of the multiverse, right? So it makes sense the TMNT universes would be synched by the origin of the Turtles within each.
- Bit of a stretch, since the Technodrome and its portal were pretty plot-relevant. But maybe the movie's writers realized they couldn't feature the Technodrome and the '87 baddies without featuring the '87 Turtles.
- It just wouldn't be complete without Mirage, or even film Turtles showing up
- Would that be the live-action films or the 2007 CGI film?
The hatred in Ch'Rell's heart formed a Heartless Shredder, like how Scar's hatred formed Ghost Scar.
- Unless taking it to the '87 universe makes the destructive power of the new Technodrome Played for Laughs
- Well, it was made in 2009, while the third cartoon and movie respectively came out in 2012 and 2014. Baring some serious time-travel magic, there was no way to include them.
Alternatively this could be the universe of some child's fanfiction.