I wish Season 5 should have a Shredder/Foot Clan storyline.
Season 4 of TMNT 2012 will start on Halloween (Oct 31, 2015). If you want some ideas about Season 4, you can write about it.
Season 4:
The Turtles and his friends return 6 months in time to collect the pieces of the Black Hole Generator/Heart of Darkness to stop the Triceratons from going to Earth.
Theory for Season 4 finale:
The Turtles, the Mighty Mutanimals, April and Casey goes face to face with Kraang Prime during a bigger Kraang invasion on New York.
Splinter, Karai and Leo takes on the Shredder and the Foot Clan for a duel.
Theory for Season 5 final episode:
Spider Bytez and the Newtralizer (if he was gonna return) joins the Foot Clan.
The Turtles, April, Casey, Karai and the Mighty Mutanimals fights the Foot Clan on a final showdown.
Shredder plans to use a super mutagen to mutate everyone in the world.
Splinter and Leo fights Shredder together.
Karai sacrifices herself by having Shredder stab her in the chest but Splinter and Leo revives her with the healing hands.
Shredder mutates into a Monster Shredder. (like in the movie Secret of the Ooze)