I like it, but there's a bit of an issue with the floor detection.
Running into something horizontally counts as being "on the floor", meaning that you can just jump up the mountain.
I would recommend either using Physics.Raycast() to check if the player is on the floor, then have "coyote frames" for jumping, or to put invisible barriers where the player isn't supposed to go (so that they can't jump on the mountain and have to use the boards)
Overall, though, really enjoyable!