Official TMNT 2 Trailer #2 Discussion

[neatoman]

OK so basically the plot is:

• Turtles are sick of hiding
• Shredder has somehow obtained Purple Mutagen
• Makes Bebop and Rocksteady and intends to make more mutants
• Turtles want to use PM to turn human

But how the hell does Kraang fit into this? He has already been shown in the trailers, so why isn't there any more info on how he fits into the plot?