I found the art on Pinterest, but the artist's signature is there, even though I can't read it very well.
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IRL!Tommy and SMP!Tommy swap universes. Not bodies, universes. Like, one Tommy poofs away and the other appears in his place.
I think that it would be hilarious if, instead of it happening in private and the others having to figure it out, it just happens abruptly in the middle of a meetup/important battle for each universe respectively. Like, it's the middle of Doomsday, Techno or Dream is dramatically taunting Tommy while the country burns around them, and then he just disappears, and an identical, less injured and traumatized Tommy takes his place, and the first thing that comes out of his mouth is something like, "WHAT THE FUCK??!!?"
On the other end of the spectrum, you have Tommy recording a 4/4 SBI meetup or something, he's dicking around and making jokes with his family friends, and suddenly he's gone, and seconds later replaced by a shaking, crying, beaten up version of himself who they immediately know is Doomsday Tommy from the ramblings he's spewing from his panic attack about dogs, withers, and explosions. They help him through it, panicking some themselves, scrap the recording, and take him home. More hurt/comfort than hilarity, but whatever.
As the SBI begin to help C!Tommy through his trauma, IRL!Tommy is causing chaos in the Dream SMP. He may or may not immediately explain who he is and where he's from, but he's sure as hell going to set stuff on fire and have fun with his newfound Minecraft powers. He will tell them eventually. More of the funnies, because Tommy knows the actors who play them and everything about them, IRL!Tommy is completely immune to whatever the SMP members throw at him. Dream trying to manipulate this new Tommy? Fuck you green bitch, I know exactly what your homeless ass is doing. Techno trying to guilt trip him for something? You told a child to die, get outta here with your victim complex having ass. Basically any time someone tries to do anything, they immediately get brutally dressed down by a child, all while he's looking them dead in the eyes. He would have a lot of fun with the Bee Duo and Michael.
I also love the whiplash that would happen between chapters. Like, one chapter Tommy is murdering somebody with hilarious brutal honesty, the next the IRL! SBI are teaching C!Tommy about the real world and having a picnic with him in a flower field or something supper sweet and fluffy like that.
The big plot twist is that the universe has a mission for them; C!Tommy was sent IRL to heal, and IRL!Tommy was sent to the Dream SMP to make them realize their wrongdoings. Double plot twist, they don't know that they have a mission. The universe doesn't tell them because it knows that it'll happen on its own.
Basically, I want to see a universe POV change between every chapter, the IRL chapters filled with tooth-rotting fluff of C!Tommy healing, like he deserves after all the shit he's been through, and the Dream SMP chapters filled with IRL!Tommy roasting everyone alive with detailed lists of everything they've done wrong while the rest of the server figuratively burns. Like a mix of comedy, angst, and pure fluff.