The counterintuitive claim in Williamson's argument can be characterized as the claim that no suitable arrangement of matter is metaphysically sufficient for the presence of a mountain (i.e., that mountains are impossible).
arrangement of matter(what Williamson is discussing as potentially making mountains)
The way physical stuff (atoms, molecules, rock, etc.) is organized and positioned in space.
metaphysically sufficient(explaining what arrangement of matter needs to do for mountains to exist)
Having all the necessary ingredients or conditions to make something actually exist in reality, rather than just appearing to exist.
metaphysics(Hartshorne's naturalistic redefinition of metaphysics)
On Hartshorne's view, the study not of realities beyond the physical, but of features of reality that are ubiquitous or that would exist in any possible world.
One possible rejoinder to Williamson’s argument would be to characterize the counterintuitive claim as the claim that no suitable arrangement of matter is metaphysically sufficient for the presence of a mountain (i.e., that mountains are impossible) and there is no reason why the negation of this proposition cannot be, on more restrictive accounts of intuition, the content of an intuition. Another possible rejoinder would point out that we have extremely good grounds for believing that there are