Disclaimer: I own nothing, if I did this is how Teen Titans Go would end.
A portal opens up just outside Titans Tower. Out comes a man wearing a red and black uniform, however his mouth is exposed. He is revealed to be Deadpool. "The Teen Titans Go universe. The other universes I killed because I was doing them a mercy from the progenitors, but this time, it'll be the other way around, apparently."
You're not going to kill them to spare them the pain? The voice inside his head said.
"Pain? What pain? These characters never went through the pain of Continuity. They deserve to die. But first, to draw them out. Where is the nearest missile bunker?"
In Titans Tower, nothing is happening. Beast Boy and Cyborg are playing a game and eating pizza, Starfire is grooming Silkie, Raven is reading a book, and Robin is polishing his staff. Robin's com beeps. "Titans, some idiot has broken into a missile bunk just outside Jump City."
"Do we have to go?" Beast Boy said.
"Yeah. It is probably just some nutjob." Cyborg said.
"Maybe. But I'd still like to see it. TITANS GO!"
By the time the Teen Titans got there, smoke filled the base. "Titans, split up!" They then split. Beast Boy sees a missile silo open up. He feels a tap on his shoulder and is punched in the face. A few minutes later the Titans gather around the open missile silo.
"Hey, where is BB?" Cyborg asked. The smoke clears and they see him strapped to a missile.
"Beast Boy!" Robin said. "Titans get him down!" but then the missile launches and they see Deadpool walk out.
"Ooh. Tough luck. He just caught the last four megaton missile back to Titans Tower." Deadpool said.
"Who are you?" Raven asked.
"Deadpool. I come from a reality really separated from yours. I killed the heroes in my universe and I have done the same to countless other realities. Now I am here to kill this universe, with absolute pleasure." They then see a bright light over where Titans Tower should be. The missile exploded and destroyed the tower. "And since Beast Boy was on that missile, I do declare him DEAD! For now you might want to return to the remnant of Titans Tower to find the remains of Beast Boy. Though I doubt there will be a body." Deadpool then disappears in a cloud of smoke. "I'll be back to finish you off soon enough."