The more I think about it, the more I realize that EM is kind of just a big epilogue of the “Came back wrong” trope.
Leo was captured a bold and determined leader, but came back scared of their own shadow and constantly apologizing and worried, crying and in pain from the different experiments and injuries they had suffered.
Casey was captured arrogant, crude and loud, but he came back quiet and stoic, barely talking for a while and rarely opening up to anyone, not wanting to bother people with his problems and reeling from his mutation.
Raph left looking for his family snappy and brash like he always is, but when he returned, he was now gentle and withdrawn, like he was scared of himself and his own temper, now finally seeing what it could cause, and desperately trying to prove to himself others that he was a good person.
When everyone disappeared, Donnie was soft-spoken, patient, and he showed his true feelings whenever he wanted. But when they came back, they found someone different who was still devoted to her family, but to strangers and beyond, she could be ruthless, uncaring, and coldly analytical.
April was a little wary of her powers when they left— now she barely uses them anymore. She used to be able to tell when she needed a break- now she never knows when she needs to sleep or eat in between her job and home life. She’s on edge, and worried about her family daily- worried that they’ll be taken away again.
And then you have Mikey. Young sweet Mikey was the heartfelt goblin of the family. He annoyed them to no end, but there was no one else who could make them smile as big. He was loud, compassionate, mischievous, and had blue eyes and a smile that could light up a room.
He came back the most wrong.
He came back cold, with the light in his eyes broken and gone. He didn’t talk, barely listened, and when he looked at you, he wasn’t trying to see what kind of person you were or how he could make you laugh/feel good.
He was looking at you to see if you were a threat, and what the most effective way to kill you would be.
He showed no emotion and refused to talk about what those scientists did to him, but the scars that now coated his body spoke volumes. And when he fought in training and a fight, he showed moves that didn’t dance around the opponent or ones you learned under a teacher. They were moves and attacks you learned when you were trying to survive.
