Frontiarme is a verb derived from the English word "front," meaning to confront or challenge someone. It's a great example of Spanglish slang commonly used in urban music genres like reggaeton and trap.
In this song, the artist uses it in the line "Dile que si va a frontiarme, que yo no cojo esa" (Tell him if he's going to confront me, I'm not having it). It conveys a defiant attitude, warning a rival not to challenge him over the woman he's pursuing.
"Faltan Pruebas" is about a secret affair. The narrator is seeing someone who already has a partner, and the whole song is built around staying hidden: they never let themselves be seen together, and the plan only works because "they lack proof."
There is real desire here ("Baby, you are mine, I eat you whole"), but also a constant awareness of the risk. The other partner is described as a threat ("that bastard") who suspects something but can't confirm it, and the narrator promises to protect the person they're with if things ever get physical.
By the second half, the tone turns more boastful and possessive, with the narrator claiming the person completely ("mine forever, like the panther in Wakanda") and dismissing the rival as finished. The song ends with the artist and featured collaborators calling out their own names, a common way to close out a reggaeton/trap track.