Ok, I think I've identified what's causing my issue, but I have no idea why it's doing this. I made a height map and terrain mask in GIMP, but when I put them into the Terrains folder, FH crashed when I clicked map maker, even though they're both in png format! I've never had this issue before, considering I've probably got about 10 or more other map things that work just fine. O.o
Another edit: Ugh. It was apparently a mistake putting them in the folder again (at least I know that those files are definitely causing problems for some reason), because even after removing them again, the game itself won't even open without crashing. Same error message keeps coming up again: 'FeralHeart.exe has stopped working'