From what I understand, the ambience mode is 99% safe of much spooky stuff - I've played for about 10-30 days in the ambient mode, and haven't found much of anything that is all that scary.
The actually dangerous/scary stuff in that mode is more often one's own stupidity and brain overreacting to things.
Frankly, I kind of find the ambient mode to be more frightening than the story mode because while the story mode has things going on, ambient means there is NOTHING out there. There's no aliens, no ghosts or goblins or ghouls or anything. Just dead silence. I've gotten so used to the spooky stuff so much that the silence scares me more than story mode at this point because I know about a majority of the scares.
I know what's out there. I've seen it all. To be sure, I get scared and shocked by it, but the scary parts have a definitive end. After something happens, I can say "wow, glad that's over" and take a breather for a second before getting back to work.
But the dark doesn't really... go away. Daytime comes around eventually, yes, but without a clock or the light breaking through the trees, the night goes on for eternity. (For all you know, it might never come again.) You can go back inside and turn all the lights on and sleep till morning, but it's always gonna be there when the day turns to evening. It's still gonna be waiting for you. Frankly, the only solution to this I can come up with is to get a massive amount of lights and put them all over the map, but... that still seems terrible, to be honest. It seems like it would just highlight how much of the dark there is, I'd only have a better grasp on how stifling the forest is. I'd merely know exactly how many trees something could be hiding behind there are in the forest, rather than having a vague, general idea.
To be honest, I kind of want DrMrNose to lean in to that aspect of the ambient mode. I want it to feel more isolated, to have more dead silence and pure, choking isolation. I feel like that's probably the best way to expand on the ambient mode, but that's just my two cents.
Anyway, I doubt ambient mode has anything scary to experience outside of the empty black that surrounds you.