Hetalia: The World Twinkle - Surprise Halloween! (2016)

It's Halloween, and America decides to invite all the other countries to his party. Since there is a costume contest, the countries show up in a wide array of outfits, although it quickly becomes clear that some among them may have taken the competition a bit too seriously. But soon, the guests begin to wonder why America hasn't shown off his own costume. What could be the reason?