Over the course of my Bob Ross journey and working my way through "The Joy of Painting" my biggest struggle early on was mountains. I, like most artists, had a hard time getting the paint to "break." I thought long and hard at how I could make it easier.
My solution, paint your base mountain color in acrylic then use your oils over top. My last painting, "Fisherman's Trail" I specifically did using this method.
First, I painted the mountain base color with a mix of crimson, black, and phthalo blue (the same colors as Bob used just in acrylic).
Once that dried I covered the entire canvas, EXCEPT for the mountain, with liquid clear. I then proceeded to do the wood background (of course now we're using oil paints).
If you had a regular painting with a sky and foreground you would cover the canvas (minus the mountain) with liquid white (or clear depending on the effect you want to achieve). Then you would proceed to do your sky before making your way to the mountain.
After your sky/background is complete it's time to tackle that mountain. Here you can basically follow along with Bob as he adds highlights and shadows to the mountain. The advantage however we have is since the mountain is dry when you start applying the highlights and shadows the canvas will really grab that paint much easier than if the mountain was wet.
I really hope someone gives my trick a try. I think you will have a much easier time with your mountains. And most of all you'll be happy with them. Feel free if you have any questions to let me know. I'll be happy to answer them.