S5's Mystical Theme
 

I've been thinking about the motivations for each season, how each one has an overall theme brought on by the impact of what leads up to it's predecessor's finale. Kraang drama in S1 caused an accident which resulted in mass mutations for S2. Their subsequent invasion at the end of S2 spawned more of the same for S3, on an even wider scale. The Triceratons destroying earth is what sent our boys into space for S4. So what in this present season is going to cause a mystical turn of events, involving dragon Gods, & other ancient evils like vampires & Ho Chan's resurrection?

I've got a theory.

The black hole generator pieces are found, the turtles undo the earth's destruction, but in the end, for one reason or another Splinter's still dead. Perhaps they then spend the latter half of S4 dealing with visions from beyond the grave, training their minds, leading up to a quest in S5 to bring him back by any means necessary. We know they're to have dealings with the lord of the underworld, at least, why else would they be meddling in matters of the hereafter if not for the sake of their father's spirit? Maybe their time travel & other spacely spectacles upset the universe's balance which puts them on their radar, unrelated to Splinter's fate, but we can't say just yet.

If not this, what do you think will bring on next season's theme?

I think the Turtles will finally beat Shredder in battle for the first time at the end of Season 4 humiliating him.

In Season 5 Shredder goes on a quest throughout the world to awaken the demons of the Foot Clan and to absorb their power, similar to IDW with Kitsune awakening the spirit of Tatsuo in his body, or the 4kids series where Oroku Saki made a pact with the Shredder demon. Or even the original cartoon where Shredder wanted the powers of Shibano-sama.

Nowadays Shredder's origins are always tied to demons or spiritual means so I wouldn't be surprised if Nick does something similar.

That's a pretty cool idea, too. Foot Mystics & all that.

I think that after something of an oddball runaraound that escalates towards the end of the season, wherein key pieces of the generator find themselves in and out of all sides hands, the Turtles will ultimately fail to prevent it from coming together at the appointed time and place.
But that, when those pieces are in the Turtles hand, Donatello or Honeycutt will tamper with them and rather than cause the creation of a black hole proper, the portal will open up and take only the Triceraton forces. An unexpected side effect of this victory will be a weakening of the walls between dimensions, allowing certain extra dimensional entities access to our realm, and after a while, access for the Turtles to theirs.

I do not think that Shredder will meet his end in this season finale, mainly because he has appeared very little for the last two. Tapping into the mystic is very much a Shredder thing to do, so I would imagine that the ongoing thread of season five will be of Shredder accumulating mystical powers, becoming a far greater threat than he has ever been and giving him ample opportunities to remind viewers why he's the series arch nemesis when he's been so quiet for two years. It would make for far more compelling viewing to take him down as the culmination of all this, rather than a quick "we owe you for that thing you did last year which by the way may not ever even happen anymore".

What if they get elemental powers!

Leo has Water
Donnie has Air
Mikey is Earth
Raph is Fire
Fugitoid is Metal

Maybe that's what it is and they have to face the foot Mystics! Even though vision quest had that, they were not exactly elements and were not very story heavy!

They already have those mystic quest outfits from visionquest we do see from time to time. And they are elemental based.

Leo has wind
Donnie Mountain
Raph Fire
and Mikey wood.

http://vignette1.wikia.nocookie.net/...20150219213616

The Fugatoid...I don't know if David Tennent will still be contracted as the Fugatoid. I think the contract only extends to these 13 episodes of the space arc. Though I can see the Fugatoid being made into the New Metalhead