I don’t want to get too into detail with the sasquatch—Amber E. Scott has pretty much covered that ground in Mystery Monsters Revisited. In particular, she offers a number of scenarios where sasquatches serve as the “villain” because they are misunderstood, victims of prejudice, or under the real villain’s control. And that’s certainly the role that works best for me.
(Then again, you could mix it up. I can imagine a really devious GM setting up an entire adventure arc where PCs prove a sasquatch’s innocence after a string of murders, only for the sasquatch to reveal he was the actual perpetrator—or guilty of far worse—all along. (“But Bigfoot, we trusted you!” “Funny, the name’s actually Bloodsmite. Allow me to show you why…”))
Since my work has pretty much been done for me, I’ll just add that the sasquatch’s primitive timelessness gives you as a number of ways to work them into your world’s ecology and stories. Are they throwbacks to Neanderthals and similar primitive humanoids? Are they a common ancestor of men and giants, before the family tree diverged? Or are they a replacement for giants on your world’s North America analogue? (One continent might have tribesmen, sasquatches, and raven-headed tengus, the other vikings, giants, and elves.) Are they, like gnomes, former refugees from the fey realms? Or are they tied to yetis in some fashion (and if so, do they guard nature from aberrations the way that yetis watch for creatures from other worlds)? Once you know the answer you know how to place them in your world and what adventures might result.
Sasquatches live in the high alpine regions, but each one must undertake a vision quest, the centerpiece of which is traveling to the seashore to find a conch or cowrie shell, from which the sasquatch will carve her personal flute (the mark of an adult). During these quests they do their best to remain hidden, but accidents happen. When a sasquatch is mistaken for a hill giant and attacked, she kills in self-defense, and a party of adventurers must decide how best to bring the creature in for trial.
The yeti clans of the Fire Alps have fallen to madness, and now their sasquatch cousins seem doomed to follow them. A sasquatch oracle makes the treacherous journey to civilization with a heartbreaking request—that adventurers aid her in seeing that the remaining members of her family, all corrupted to the worship of the Old Ones, are put down.
Young adventurers are training to join the Ash League, a group of rangers, druids, barbarians, and other wilderness-focused specialists that defend the Northwood. (A cluster of ash leaves is the organization’s symbol.) One of their tests is to bring back proof of a sasquatch sighting (pitting their skills against the ape-man’s +14 Stealth).
—Bestiary 3 236
I got my first ever piece of fan art! ArtisticLicenseToKill served up a My Little Sagari that shall haunt my dreams for days to come.