Get up to raton canyon area around mount chiliad, that's where this whole yeti business happens and timing is critical here. You'll need to track down exactly five clues between specific spots: there's this deer carcass by the river with distinct claw marks, some body parts under a broken tree nearby, a bloody shirt close to an abandoned vehicle, a wrecked car beneath one of the bridges, and a tent setup on this mound that overlooks another bridge. The game actually helps you here, when you're getting close to any clue there's this distinct throbbing sound that gets stronger, so follow that rhythm.

The real technical part comes with the actual yeti encounter though. You absolutely need to wait until nighttime, specifically between 9 pm and 6 am in game time, and you need all five clues collected first. Watch your minimap carefully for a red skull marker, that's your target. If it's not showing up right away just patrol the marked area systematically, it'll spawn eventually. The thing about positioning here is you want to keep enough distance to react but stay close enough to keep it from despawning. Good to know: each clue investigation pays out 10k, so there's that bonus while you're hunting.

Getting that yeti outfit unlock means being thorough with the hunt, don't skip any clues or try to rush the nighttime encounter. The sound cues are really your best friend here, especially when tracking down those initial locations, so maybe turn up your game volume a bit.

Important: the yeti event only happens during winter in real life or christmas events in the game.