Whirling rocks consumes usages extremely quickly compared to competitor spells for its effects, and I found it to be less effective than stone form at doing the same thing despite stone form synergizing with mountain stance much better (whirling rocks doesn't work with mountain stance except on the turn you toggle it for the saving-you-charges effect). I found it to be underwhelming compared to stone form and earthquake, which I loved. It didn't really feel worthy of level 4 for its effects.
For a level 4 spell that takes a lot of work to get to, I feel like the spell Rock Eater should let you eat bricks, not just stone chunks, which are seemingly rare in actual levels - letting you eat bricks would also have it synergize with the other rock spells. Maybe that'd be too powerful, but then again, it's currently pretty easy to get your hands on a life-stealing sword very early that heals you for insane amounts whenever you hit / kill things, so compared to a level 4 spell, I feel like the level 4 spell shouldn't require me to have a mine or something at home making stone chunks that I can eat to heal, and taking them into missions with me knowing i'll have trouble refreshing them while I'm in the missions, when at that point I could just be buying health potions or something.
Unless I'm missing something and there's some easy way to get stone chunks inside of missions.
As for mountain stance, I believe when unupgraded it is bugged. When upgraded you're supposed to be able to get as much as a 50% chance to refund spell casts when using it. In my experience, at level 0 before upgrading it, you get a 100% chance for it to refund spells when using it (which I used to great effect in my last run), and only after upgrading it does it downgrade and become less effective (25 or 50% chance respectively).
I think there's also a bug with cold aura where it freezes enemies around you solid, I had it reliably happening for an entire run using it, but my next run it didn't happen. At first I assumed that was the intended behavior but now it is nolonger replicable so I'm unsure what was causing it. If there's some intended effect where cold aura actually is supposed to freeze enemies solid, it's possible I was triggering it and it's not a bug, but if there isn't, it certainly seemed to be. It may be some interaction between cold aura and frozen weapon, but it could also be unrelated.