I made a mountain pillow the other day with things I found from the thrift shop. It was relatively easy and you can do it too!
Step 1: What you'll need + pattern cutting
I used: a green pillow cases from the thrift store, one small (10" x 30" or so) white & textured piece of fabric I found at the thrift store, a large sheet of newspaper for the pattern, a sharpie (a dark pen will work too), scissors, my sewing machine, some poly-fil, and an always trusty needle and thread.
First, you'll need to draw the pattern. I honestly just sketched one by hand. Cut it out and lie it on top of one of the pillowcases. Pin the pattern to the pillow case and cut.
Now cut the snow part off of the pattern, pin it to the white fabric and cut it out. (If you can tell, I cut two of them and that's only because I'm making two pillows.)