Calaca literally means “skeleton,” and in Mexican and broader Latin American Spanish it is also a playful or folkloric nickname for death, similar to “the Grim Reaper.” In the song, “se los carga la calaca” means that death will come for them, making this unusual word especially vivid and memorable.
"Tigre De Vengala" is Costa Rican rapper Dorian Ampie playing the kid who grew up too fast. He tells you so himself: "Hace rato se fue el niño que veía al Hombre Araña" [The kid who watched Spider-Man left a long time ago], and now he is "ese chamaco que sale en pasamontañas" [that kid who goes out in a ski mask]. The whole track is street bravado about rivals, guns and money, and it does not pretend otherwise.
The slang is where the fun is for a learner. Fierro (literally "iron") means a gun, and la flaca ("the skinny one") is death, which is why "La flaca se avecina" [Death is drawing near] lands so coldly. La calaca is another name for death, the skeleton figure. Chamaco means kid, una vuelta is a job or a deal, and plata is money. He is also openly paranoid: "Camino desconfiado, me asusta mi propia sombra" [I walk around distrustful, my own shadow scares me].
The title comes from his best boast: "Yo soy solo un chamaco pero puedo contra todos / Como el Tigre de Bengala aunque veinte sean los lobos" [I'm just a kid but I can take them all on / Like the Bengal tiger even if there are twenty wolves]. Note the song spells it with a V, the way it sounds in Spanish. It is a bit much, and that is the point. He also says he is "un tiburón en un mar lleno de peces" [a shark in a sea full of fish], so expect plenty of animal metaphors for being the toughest one around.