Based on the translation "Sinister Phenomenon" (or "Ominous Phenomenon"), this sounds like a feature for a horror, thriller, or supernatural investigation TTRPG (like Call of Cthulhu, Delta Green, or Monster of the Week).
A halo-like rainbow that appears around the shadow of an aircraft. Historically, mountain climbers who saw this "shadow person" surrounded by light felt they were witnessing a supernatural omen. fenómeno siniestro
Sometimes, nature produces sights so rare and strange they feel "siniestro" even if they are purely physical. Based on the translation "Sinister Phenomenon" (or "Ominous