Malamente is an adverb that literally means "badly". While you might often hear the word "mal" (bad), malamente is a more intense and stylistic choice that ROSALÍA uses to set the whole tone of the song.
The song's subtitle is "Augurio" (Omen), and the repeated chant of malamente creates a haunting feeling of a bad premonition. It's not just that something is bad; it's that things are unfolding in a bad way, as if destined by fate.
Have you ever had a really bad feeling about something? That's the whole mood of ROSALÍA's "MALAMENTE". She opens with this perfect image of a premonition: "Ese cristalito roto / Yo sentí como crujía / Antes de caerse al suelo / Ya sabía que se rompía" (That little broken glass / I felt it crack / Before it hit the floor / I already knew it was breaking). The song is full of these spooky signs, from a flickering light to a wobbly bridge in a dream. It's all building up to a feeling of "Malamente" (Badly), a word she repeats like a dark chant.
But this isn't just a song about being scared. After all the warnings, including one from a fortune teller, she decides to act. She says, "Aunque no esté bonita / La noche... / Voy a salir pa' la calle" (Even if the night isn't pretty... / I'm going out to the street). She puts on her jewelry like armor and says a little prayer for protection. The final line reveals what this is all about: "No voy a perder ni un minuto en volver a pensarte" (I'm not going to waste another minute thinking about you again). It's a song about breaking free from a toxic situation, even when every instinct tells you something terrible is about to happen.