The peryton is a monstrosity with the body of an enormous bird of prey and the head of a stag, albeit a carnivorous stag with nasty incisors. Perytons roost in mountains and rocky hills near settled areas where they can find prey. According to the Monster Manual, they favor humanoids in general and humans and elves in particular, and they’ll often try to rip out their prey’s heart and carry it off. “When attacking a humanoid,” the MM says, “a peryton is single-minded and relentless, fighting until it or its prey dies.” This is the behavioral oddity that distinguishes it, as a monstrosity, from an ordinary evolved creature.
All of a peryton’s physical abilities are above average, but its Strength is especially high, so it’s going to go for big-damage attacks, either by dive-bombing its prey or in a close-quarters scrap. Its features include Dive Attack and Flyby: the former is an aerial charge that deals additional damage, while the latter exempts it from opportunity attacks when it flies out of an enemy’s reach. The peryton has a flying speed of 60 feet, and its Dive Attack requires it to fly 30 feet to gain the extra damage.
This combination makes the peryton’s preferred attack tactic obvious: Its first attack will always be a Dive Attack, from a distance of exactly 30 feet if possible. It uses 30 feet of its move to conduct this attack; Multiattacks (action) with Talons and Gore, gaining Dive Attack damage on both of these; then, if its target is still alive and kicking, uses the other 30 feet of its move to fly away again. As long as its prey lives, it will repeat this half-move/Dive Attack/half-move combination.