Those mountains are better, but even with the perspective change, I'm not sure that they match the trees… At least if you plan to use the first style, I noticed that they look different in the last pics. But I think the first is so unique and cool that it would be a waste not to use them!

Trying to think of what sort of mountains would fit… The trees are very much silhouettes, single color shapes that overlap into interesting patterns. What if you'd draw the mountains in the same way? Not as just one big triangle maybe, but compose each mountain from sharp color blocks? I'll try to illustrate what I mean if you want, I'm not the best at explaining things