Major Wish

Std, costs a whole soul; you speak a wish, and your planar patron grants it, claiming the soul in return. The soul must be offered freely — your own, or that of a willing (or contracted) donor. This is essentially the spell Wish: it can cause permanent bodily changes (including resurrection), create permanent objects (even magic items), duplicate any normal power of any level, etc.

The patron interprets the wording of the wish; careless phrasing invites a devil's reading.