Wavy-tile wall is a wallpaper. Source: Nook's Cranny. It costs 1,740 Bells and sells for 435 Bells. It can also be bought for 1,600 Poki (Happy Home Paradise). Happy Home Academy themes: shop and facility.
Where to get it
Nook's Cranny: Timmy and Tommy's store on your island, with a daily rotation of furniture and clothing alongside staples such as tools and seeds.
