So I only have the beginning planned out but anyway~~
Instead of Leo and Mikey sendign Casey to the past its Raph and Donnie
Donnies built a time machine with mikeys help before he died and Raph, Donnie, and Casey are racing towards it- humanity has no hope the resistance has lost
But the bad part is it doesn't work without a massive amount of ninpo which mikey only possess
So in order to fix everything and save humanity Raph and Donnie hookthemselves up to the machine and send Casey to the past.
We then see the same argument between Raph and Leo after the key was lost, but this time we see Mikey and Donnie arguing before.
In "Donnies gifts" Donnie goves Mikey that jumpsuit that inflates whenever mikey does his razzmataz. And again when they lost the key we see Mikey using his razzmataz. He's worried about Mikey being safe, and wants him to take better care of himself. Whereas Mikey wants Donnie off his back.
Thats all I got lmbo but I know that Raph and Leo fighting are going to be the subplot and Donnie and Mikey are taking their places in the movie.
Raph takes Mikeys in a way
That was a lot thaks for asking!!