Jamieson, Fausset and Brown on Ezekiel 31:18

18. Application of the parabolic description of Assyria to the parallel case of Egypt. "All that has been said of the Assyrian consider as said to thyself. To whom art thou so like, as thou art to the Assyrian? To none." The lesson on a gigantic scale of Eden-like privileges abused to pride and sin by the Assyrian, as in the case of the first man in Eden, ending in ruin, was to be repeated in Egypt's case. For the unchangeable God governs the world on the same unchangeable principles.

thou shall lie in ... uncircumcised--As circumcision was an object of mocking to thee, thou shall lie in the midst of the uncircumcised, slain by their sword [Grotius]. Retribution in kind (Eze 28:10).

This is Pharaoh--Pharaoh's end shall be the same humiliating one as I have depicted the Assyrian's to have been. "This" is demonstrative, as if he were pointing with the finger to Pharaoh lying prostrate, a spectacle to all, as on the shore of the Red Sea (Ex 14:30, 31).