#undershell

Overshell-- (originally Undershell, but choosing to use that title for a different au) an au in which Frisk and the underground monsters meet the tmnt and co. The tmnt try to convince the monsters to stay away from humans, Frisk makes it their #1 goal to bring monsters, humans and mutants to unite and live peacefully together. Needless to say, many mutants have their doubts on how possible this is.

Undershell-- somehow the Kraang manage to chase Master Splinter out of the city instead of into the sewers. The chase him up Mt. Ebot (which is actually not supposed to exist in that earth, in any of them, but more on that later) and in a last-ditch attempt at protecting his boys and himself, leaps into the hole to the underground.

The Kraang, of course, follow him in and there he is aided by Toriel, caretaker of the ruins. After defeating the Kraang, Toriel takes Splinter to her home where they have a good long talk about how he ended up in his situation, about the underground, etc. Somehow Toriel finds out about his human soul, (having assumed he and the tots were fellow monsters before) and tells him he can NEVER reveal his soul to anyone, or else he'll be hunted and killed.

This all takes place 13-14 years before Frisk's arrival, so still some time before the events of tmnt 2012 begin. Toriel helped the Hamato clan get into the legal system records and thus Splinter was able to open up a dojo either in the city or in a small town unreachable to Frisk during the main game.

The boys grow up believing they're all regular monsters and Master Splinter becomes somewhat reclusive, not really speaking to others very often aside from his sons, students and parents of students.

Of course, this doesn't last forever and the boys do end up having some contact with Frisk and the rest of the main cast.

Also: the brothers find out that not only are their souls neither monster nor human, but also that that can easily pass through the barrier on their own, something they unanimously decide to keep to themselves until they figure out why.

Endingshell-- the last and probably final of my ut/tmnt aus, mostly involves my outcode Donnie, Static!Donatello.... Which is still pretty under developed. But basically, he keeps trying to save Mikey, who's been possessed by Chara, but keeps failing. He resorts to going from au to au stealing human and animal mutant souls alike in an attempt to become a god and save his bro. He's also got a huge soul-separating machine he's building in the anti void. (Being in the anti void also is slowly eating away at his sanity. He continuously keeps rejecting the kind offers of company and hanging out of the kinder anti-void residents. I.e, Core Frisk.)

The main souls he's after are kindness and integrity souls.

He combines his power and knowledge with a Gaster's soul, giving him many of the same abilities as Sans. I.e, teleporting, gaster blasters. But he does not have the Karma ability, however. This team up happens after Gaster and Static!Donnie make a deal of some sorts.

Donnie cannot use gaster blasters without the use of Gaster's soul. Solo, Static!Donnie can make machinery glitch out and anything with speakers or screens produces mostly static when he is present. Thus where he gets his name.

Static!Donnie is an adult, not a teenager. He tends to take the shape of a slightly older version of whatever Donatello resides in whatever au he's in. His true form, however is somewhat melted looking and skeletal, with glitchy code bits like Error Sans and Geno Sans.

Speaking of which, Error naturally considers him to be an abomination and wants him and all the tmnt au's destroyed. Ink however, is fascinated and even excited at the idea of these new, strange au's he never new existed. It's like he's been given access to a whole new multiverse! (He has)

And (maybe) Core Frisk.

You know that episode in tmnt 2012 where April basically disintegrates Donnie from existence?

Well. That gives him his first look at the anti-void, where he meets Gaster. Has a conversation with him. But he totally forgets it and him when April reassembles his molecules.

He occasionally has odd dreams about this odd white void and the utterly blacker than black shape he sees there. But they're always blurry and the dreams soon fade away after he wakes up.

That is, until a certain moment with Sans (and (maybe) Papyrus and/or Alphys). Something starts tugging on his mind. Little thoughts and feelings of being watched and like he's forgetting something.

I've seen quite a lot of undertale crossovers where some characters replace the original ones and while crossover's like are all fine and dandy, they're really not for me as a majority of the time (not always) i find them to be boring.

So in Undershell/Endingshell i'm going to have the characters from both worlds meet and interact n' stuff.

Frisk will make some people uncomfortable with their flirting. Tori will mom the turtles. Maybe have some Asgore x Splinter, because they both deserve to be happy and I just love shipping Asgore with other dad characters.

Metta will probably end up endangering both monsters and mutants because of his need be seen and in the spotlight.

Frisk keeps trying to get Shredder's lackies to convert to the good side.

NO ONE CAN ESCAPE FRISK'S INCREDIBLY TONED GAYDAR.

Alphys and Donnie teaming up for stuff. (I.e. rescue missions, building robots, saving the world, etc.)

Undyne can straight up fucking lift Slash + Leatherhead and this is unsettling to them at first.

The tmnt gang all learning about the different kinds of souls, what that means and such.

An entire episode/chapter centered around the Mad Dummy possesing/replacing one of the turtle's training dummies. (Or maybe an entirely new ghost oc?)

Sans's puns, Sans driving everyone up the wall with said puns. Tori, Frisk and Mikey driving everyone up the wall with puns.

(And maybe (maybe) Sans vs Shredder?)

THE GREAT PAPYRUS trying to befriend the enemy and convince them to join the good side and ultimately failing.

Onesided Mettaton x Bishop flirting because I find it funny.

On the note of things i find funny: Frisk refering to Leo as dad occasionally just to mess with him. He protests at first but later gives up.

Aight so i think I figured somethin out.

For the last few weeks i've been trying to figure out how I want to do Undershell, my undertale/tmnt crossover.

I mostly wanna do it to give my special au Donnie and Mikey a backstory.

I call them Static!Donnie and Murder!Mikey, who were heavily inspired by Error!Sans, Core Frisk, Classic Sans, Dust!Sans and Killer!Sans.

More on them later.

I've decided that Endingshell will be the bad ending that splits off from the regular Undershell timeline, which will already have its three neutral, genocide and pacifist endings.

I also wanted to figure out a similar au Leo and Raph but I still need to brainstorm those two.

But Endingshell will either be the sequel to Undershell or Undershell will be the prequel to Endingshell.

Alright since i still haven't posted anything on Undershell yet, here's some hc's about the tmnt characters souls.

Animals have octagon shaped souls, so the turtles, Leatherhead, and Slash have octagon souls, while anyone who used to be human has the heart shaped soul.

Mikey has a green, kindness soul.

Master Splinter has an indigo, integrity soul

Leo and Slash both have Yellow Justice souls

Raphael has the Bravery orange soul

I wanted to give Casey a justice soul and April a bravery soul but I'm wondering if I should either switch the colors or make them both bravery?

Donnie I'm going to give either patience or perseverance, but I'm leaning more towards perseverance.

Kurai has an integrity soul like her dad.

Shredder has a determination soul. Chara wants this soul.

Not sure what kind of souls to give the Kraang yet. Maybe blank, greyish orbs? Except for Bishop. Bishop's soul will have color.

Mondo Gecko will have a perseverance soul.

Tigerclaw has a patience soul.

I'm going to go ahead and add some new colors and soul traits for some characters

Zephir's soul is turqoise for loyalty... That's all I got rn.