Image: UbisoftOfficial screenshot from Ubisoft.
Ultimate Predator asks you to hunt every Mythical Animal on Yara. It only counts in the solo campaign, and the beasts drop parts that trade for unique gear.
Build the Hunter's Lodge at a Guerrilla Camp and upgrade it to rank 3. Buy the Hunting Brochures for the mythical animals, travel to each marked spot and kill the creature. The trophy pops once every mythical animal is down.
Bring heavy firepower, since these animals hit much harder than normal wildlife. The rank 3 lodge also means fire, bullets and explosives no longer ruin meat, so use whatever works. Mamutito on Isla Santuario is a good first target before you head to the other regions.