Well... if you want to get into really funny business, white could promote to a black Rook on its home square (not valid with current FIDE rules, but older rule

Well... if you want to get into really funny business, white could promote to a black Rook on its home square (not valid with current FIDE rules, but older rule sets weren't always specific about the color of the piece promoted to). I don't think you should castle with that Rook, but maybe? I guess something about being on the squares since the beginning of the game.