do you have the huge wallet? If you do go to North clock town at midnight on the first day. when the robbery takes place, hit the thief with your sword. Now skip over to 10 on the final night and go to the curiousity shop. go inside and purchase the mask (I'll save it as a surprise) for 500 rupees. if you don't have the huge wallet, look up "oceanside spider house" on google. its pretty complicate