"High Desert Kill" (1989 TV-film)?
Här är en sammandrag från IMDb:
Like every year, Jim, Ray, Brad and Paul leave the town for a week to go hunting in the woods. But this year everything is different: There's not a single animal to be found, the whole forest has fallen quiet. Two female campers they meet have mysteriously disappeared the next day, leaving their whole equipment behind. And then they start to behave weird themselves... An alien power is using them for cruel psychological experiments.
Här är hela filmen från YouTube, scenen med form-shifter som visas i ett fönster i form av en karaktär som dött tidigare börjar kl. 1:29:00.