I would like to paint a mountain scene on fondant and have it look like an oil painting. Any tips on how to do this? TIA

You can mix petal dusts with clear alcohol (vodka, gin) and then paint onto the fondant. I believe that you can also use gel food colours (probably more oil-like) to paint directly onto fondant. These would likely take longer to dry.

You could experiment on a piece of rolled fondant to see which effect you prefer before you actually do it on the cake.