Here's the basics of the trilogy I thought of (my feelings won't be hurt if it's not liked)
1st: Krang and Shredder find Godzilla's skeleton after he was killed in '54 and revive him. They also find four legendary Earth monsters in hibernation: Gamera, Baragon, Anguirus, and Varan and plan to use them with Godzilla to raise the Technedrome from the center of the Earth. The Turtles intervene and while they don't stop Shredder from releasing the three dinosaurian creatures, they are able to get the pendent that connects them to Gamera. With Gamera's help, they break Shredder's hold on Godzilla and defeat the monsters.
2nd: Krang, realizing that they not only have the Turtles in their way but Godzilla and Gamera as well, releases Megaguirus and Legion (and their respective swarms) into the city from Dimension X. Krang also reveals that the Oxygen Destroyer is also a weapon found in Dimension X as well and plan to use it is in someways. While Godzilla and Gamera join together to fight Megaguirus and Legion, the Turtles call on all their allies to help destroy the respective swarms. After the insects are defeated, Krang reveals he fixed the chip that enables to him grow and enhances the suit to take on Godzilla and Gamera himself. The Turtles infiltrate the suit to destroy the chip for good while dealing with new defenses. Before the Turtles destroy the chip, Krang injects Micro Oxygen into Godzilla.
3rd: Godzilla is dying from the Micro Oxygen but wants to so he can rest in peace. Krang brings a baby Iris from Dimension X and gives Shredder a pendent to control the creature. Iris however needs to bond with another creature, so Shredder decides that April would be the perfect one. And to keep Gamera and Godzilla away from Iris, Krang brings out one of his cyborgs: Gigan. During the first attack the Turtles prevent April's capture and Godzilla and Gamera are able to tear apart Gigan. Before Gigan is completely destroyed Krang returns him to Dimension X for upgrades and Iris latches onto Godzilla and sucks more of his energy away in order to become an adult. Shredder attempts another capture of April and succeeds. Before the Turtles can save her, Iris absorbs her into its body, bringing the creature up to full strength, and Shredder orders it to bring the Technedrome back to the surface in the middle of the city. Gamera and a severely weakened Godzilla try to prevent it but an upgraded Gigan is unleashed to keep the monsters busy. Soon Iris appears back in the city with the Technedrome in its tentacles. While the other Turtles infiltrate the Technedrome to shut down the weaponry, Leonardo tricks Iris into absorbing him and slices April free. Without April, Iris weakens, allowing Godzilla and Gamera to defeat it and then destroy Gigan once and for all. Before the Turtles shut down the weapons, Krang fires the laser cannon, tearing into the near-death Godzilla. The Turtles escape before Godzilla, in his dying breath, turns his anger upon the battle station and sends the Technidrome back to the center of the Earth. It concludes with Gamera returning Godzilla's body back to the ocean and himself going back into hibernation.
What do you think?