Michael Morris
First Post
The caster may throw the stones (Magic attack bonus), or hand them off to be thrown by others (Strength attack), or they can be shot from a sling (Dexterity attack).
Mechanically and narratively, it's kinda uninteresting. You're THROWING BOULDERS, and it's a ninth level spell fer chrissakes. It's okay to be complicated. Have them shatter or bounce, striking a small area each, then leave behind difficult terrain.
(Plus it should have flashback! j/k)