If they can cross over with 2012, 2003, 1987 and comic tmnt.
That mean there must be Dimension X with Krang or other. It's no surprise as Dimension X inhabited are highly advanced technology of crossover like 2012 got into 1987 when Krang tired destory many as we know. Or Krang with 1987 Shredder invade 2012.
I not too sure that Krang or Kraang but I sure there should being other alien in Dimension who got into 2018
Don't take serious. This is just threoy and yet they can crossover without Dimension X but I letting you know about it