During wintertime, go over to an igloo (try early January). Leave all your items behind (like just dump them in the ground outside of the igloo) and also leave behind most of your money so you only have 3000 Bells (you can have more if you're willing to lose more). If you're lazy, just attach your money as presents to letters in your inventory. Now, talk repeatedly to the person in the igloo. Every once in a while, they should ask if you want to play a game where you buy an item of theirs for an amount of money you will play for. If the item name is DUMMY, say yes, if not, decline (unless you want the item). Now, play the game and get the DUMMY item. It's a tester item that the programmers supposedly forgot to remove from the game. You can put it in your house... it doesn't do much. It's a white triangle with "DUMMY" written in read on it, in Japanese. Tom Nook will not buy it from you.
Submitted by: kornyhatemachine