Mamagrano is a highly informal and somewhat aggressive slang term, similar to "motherfucker" in English, used to express strong disbelief or challenge.
In the song, Eladio Carrion uses it when he asks, "¿Uno mejor que yo? Mamagrano, ¿qué te hueliste?" (Someone better than me? Motherfucker, what did you smell?). This phrase conveys his supreme confidence and dismisses any notion of someone being superior to him, making it a memorable and impactful word choice within the lyrics.
Eladio Carrión runs this whole song out of a kitchen. He is the chef, the verse is the plate, and the table eats whatever he cooked: "Chef Ela, siempre viran por cómo cocino" (Chef Ela, they always turn around for the way I cook), "Comen mi comida, nunca están arrepentido'" (They eat my food, they never regret it). A branzino is an expensive fish, and the flex is in who gets served — "Yo cociné, pero me sirvo ahorita, come tú" (I cooked, but I'm serving myself first; you eat).
The other half is a ten-year argument with everyone who doubted him. "Van diez años dándole, no se va al hambre" (Ten years at it, and the hunger still doesn't go) — hunger is the one appetite he refuses to feed, because it is what keeps him in the booth. He repeats his own pep talk, "'Tú eres el mejor', todos los días me lo digo" ('You're the best,' I tell myself every day), then draws the line in the same breath: "creo en mí, no soy creído" (I believe in myself, I'm not stuck up). Big Sean takes the last verse in English and keeps the menu running — "Branzino, my favorite note is a C note" — trading Puerto Rico for Detroit without changing the appetite.