You now have smash mode (scroll for your cursor to change). Go around whole Biscotti and smash all the barrels - some are golden and give solid money, some hide a lever/chest/etc.
After that in order to escape Biscotti through the tunnels you need to enter the windmill from it's backdoor. Go inside of the abandoned cabin on the far right and little up of Biscotti, look for a wrong-colored leaf, tug it with normal cursor so a ladder would drop, on the "second floor" smash the rocks to find and press the button for another ladder to drop. After that you'll find a way into the windmill and there's a crawlspace into Biscotti tunnels that eventually lead outside of Biscotti's black bubble.
Last part of the game right now is Nightmare's Night Domain, where you finally fight Nightmare herself and where yellow seal is located.