From GameWatcher: “Outward doesn’t beat around the bush when it comes to survival. As beautiful as Aurai can be, it’s also a deadly place that will murder you in an instant. That’s why, it’s a good idea to look towards increasing both your damage output and resistances. If you’re having trouble with Decay damage, the Outward Possessed Boon is quite handy to have.”
Source: N4G PC Outward Possessed Boon Location – Where to Find the Possessed Boon