Based on the clues "ovni" (UFO) and "hombre de negro" (man in black), the most likely is:
If you are stuck on a different number of letters, you can find updated lists for all levels on community sites like the 4 Fotos 1 Palabra Solution Guide or 4Fotos1Palabra.pro . 4 fotos 1 palabra ovni hombre de negro
Good luck, agent.