Evil Sentient Forest

branches moving and touching the PCs backs as they walk, they look back and the trees look completely normal.

something like this: https://www.youtube.com/watch?v=njTmKCPEXwY

would be pretty cool
additionally hearing knocks of wood on the trees, having branches of trees falling on PCs heads, etc

Make the forest inhabited with Fey like dryads and pixies that interpret themselves as daughters of the forest. Make no mention of them at all for like the first couple sessions to lull the party into thinking they're utterly alone, then spring one of them on 'em, making it seem like a friend at first. But of course, Fey are totally amoral, so shit goes down.

you cant get spooked when you are in group
/thread

>>54216334
something like pango, all the trees are just shoots from the same sentient root system.

You may try creating areas where the party has an easy time going deeper into the woods but an awful time leaving. See: sawgrass, briars. Maybe the trees can move slightly to disorient the party. Or the trees produce burs that can stick in flesh and slowly tap roots into it.