This page of the guide to Far Cry 6 features the location and description of the fight with the mythical animal Black Demoníaco.
Subregion: Aguas Lindas.
District: Ida's Refuge.
The Black Demoníaco lives in the forest, along with other wolves. You will also come across the White Demoníaco at this location. Wolves protect each other and can heal themselves. You must act quickly and decisively. It's best to attack silently from a distance, e.g. with a bow or a sniper rifle.