There's a curious, cheap technique i'm in love with that can help you with the icy rocks. Take a piece of bark (yep, from a tree!) or a traditional cork and clean it with anything not-water-based (like ammonia) to prevent the water to create moss. Then, glue the bark to the base and paint it like a rock. A few tones of grey and drybrush will do the trick! After that, use glue to create stalactites from the corners. I usually cut a few random pieces of the original mold of the miniature to create ice chunks, but this usually works better with "magic" ice, because its pretty weird to see natural giant crystals popping out of the dirt.
I'll put you a video that shows the whole process. I hope you enjoy your icy enviro!
Rock making (just do it a bit lighter, with more greys than browns)
https://www.youtube.com/watch?v=jqfYE4ZfEMc
Snow effect:
https://www.youtube.com/watch?v=W67IOg4HqQ0&list=PLPnYU7LtP7-H7zLZrFB9f9FuKZ0F4_ASi&index=7