He'd be the kind of friend who: Tragically never bettered himself
It used to be fun to hang with Mario, y'know? He'd always been such a happy guy, and the two of you made a ton of wonderful memories together over the years. But you moved on, while he stayed behind. You traveled the world a bit. You lived. Then, when you went back to visit your old pal, you were sad to discover that he hadn't pursued any sort of self-betterment. For him, that place was all he'd ever known. He couldn't leave.
Mario wore the same familiar clothes, smelling of that same familiar sewage stink, telling the same stories he'd always told. He was starved for conversation but had nothing new to say. "Did I ever tell you about the time I saved Princess Peach from Bowser?" he asked (for what, the hundredth time?). "Yeah, man..." The two of you took a drink in awkward silence; you, a seeker of worldly knowledge, and he, a simple man stuck in a place he could never escape. You left after a few drinks, but looking back through the yellowed glass of that dingy old bar, you saw him order another round by himself.