My cube has ended up in a position where I need to swap the corners diagonally across to finish the cube. However to my understanding this is impossible. Is there another way to solve this? I tried taking the cube apart but the corner pieces are stuck on this particular one. Note that it is the Ghost Cube Black variant. Help me, thank you.
Copy-pasted my comment as an answer on request of @Rubio♦:
There are two pair of pieces that are very similar on the Ghost Cube, so you've probably swapped those pieces by accident causing the issues with the last two corners you have now. I don't know which brand of Ghost Cube you have, but make sure everything you've already solved is completely flat. Most likely one of those triangle-shaped corners are swapped (that's usually the case when I solve mine). But it's also possible the three (corner-edge-corner) that are similar are all swapped together.
link to comment
Pictures (of each of the six sides of the Ghost Cube) would help, though. That way we might be better able to pin-point the problem.