Been trawling the 'Regular Show' tags on AO3 for ages, and the Mordecai x Margaret fics that actually stick with me are the ones that feel like they could be lost episodes—not just romantic fluff. 'Analog Signals' by cartunes is my absolute top rec. It’s a slow-burn post-graduation AU where they reunite at a failing record store, and the author nails the awkward, unresolved tension that the show left us with. The dialogue has that specific blend of melancholy and dumb humor the show did so well.
What sets it apart is how it treats Mordecai's self-sabotage not as a joke, but as a genuine character flaw he has to work through, while Margaret's ambition isn't softened. They feel like real adults, not just cartoon characters. The supporting cast pops in perfectly, too—Rigby’s cameo had me cackling. It’s less about grand declarations and more about two people figuring out if their wavelengths still match after everything. The ending is bittersweet but hopeful in a way that just fits.