I'm very sorry for not finishing this story. My problem is that I get these great ideas in my head for long stories, but I don't really commit to taking the time to write them. Life keeps moving forward. Both shows have run their course, Regular Show in particular. More content has been added to both shows that this fanfic is WAY out of date on. I finished college now, and need to start thinking about my life and career, and would rather spend my free time doing other things besides writing fanfics.
Here I will summarize what happens in the rest of the story, giving some long overdue closure.
Many crazy adventures happen while Mordecai and Rigby are at TUFF. At the bar, Rigby and Roger get sucked into a video game while Mordecai, Dudley, and Phil have to get them out. One arc involved a villain known as Scare-Raven (based on Scarecrow) flooding the town with fear toxin on Halloween, with Mordecai, Rigby, and Dudley being the only survivors to fix it. One arc would have Mordecai living with Blue and working with Kitty while Rigby lived with Red and worked with Dudley. One arc had Carl the Llama in prison, with Kitty, Mordecai and Rigby interrogating him, him being a sort of Hannibal Lector esque character. One arc would have a bunch of death traps set up by The Puzzler. One arc would have Mordecai and Rigby going back to the park to catch up with the others, showing off how well they've been doing, and then hosting a big rave party for all their friends, which Margarette would not show up to because she's been kidnapped. One arc would involve a mutant venus fly trap infecting the park, and TUFF would have to team up with the park workers to stop it. At one point Red and Blue would steal a TUFF car like in that one episode of their own show.
The villain seen at the end of chapter 4 was a bear named Boskov Medved (clever name, as Medved is the Russain word for bear, and also is a nod to Dmitry Medvedev, the third president of Russia), a Russian Arms Dealer who was to serve as the main antagonist of the story. He owned a company known as Medved Industries, which had sold weapons and equipment to all the other minor villains of the series. He had a divorced wife named Margosha and a daughter named Duscha. Rigby would have started dating Duscha for a while, and one arc would involve him going to Boskov's house for dinner. He'd have this master plan somewhat inspired by Watchmen, and need a rare element known as colossium. Dudley would be mortally wounded, and be out of commission for a few arcs. Eventually Medved would capture Margarette and use her as a bargaining chip. Mordecai would have to trade the colossium to save her.
After Medved and his company were defeated, Mordecai and Rigby decided they had enough of the spy life, and quit. Deciding they had proven themselves by working at TUFF, Benson hires them again. Mordecai and Margaret get together, Dudley and Kitty get together, and most likely Rigby and Duscha would break up.