Good-Feel, developer of Yoshi and the Mysterious Book, has been confirmed as the team behind Yoshi's Woolly World, Princess Peach Showtime, and Kirby's Epic Yarn.
Perhaps more than any company other than Rockstar, Nintendo is one of the most secretive developers in all of gaming. Not only do we rarely know what it's planning for the future (well, unless someone leaks those plans and it seems to change them in response), but we often don't even know exactly who it is. to make Games that have been announced.
For the past few years, it's been a running theme that, outside of games like Donkey Kong Bananza where it's too big to ignore, Nintendo doesn't tell anyone about the dev teams working on any project until the game is actually out. It happened once again with Yoshi and the mysterious book, even though most of us had a pretty good idea who was behind it.
Surprise surprise, Good-Feel is the team behind Yoshi and the Mysterious Book
The Princess Peach Showtime devs are back for another low-key Switch game
Although Yoshi and the Mysterious Book doesn't release until tomorrow, reviews for the game dropped earlier this week, meaning that a lot has been shared about the game online. As pointed out by My Nintendo News and originally highlighted in VGC's review, one of the revealing things about the game is its developer, Good-Feel.
For those who don't know, Good-Feel is the team that developed Yoshi's Woolly World (as well as the Switch port, Crafted World), Kirby's Epic Yarn, and, most recently, Princess Peach Showtime. Given Mysterious Book's chill vibes, unique art style, and gameplay similarities to Woolly World, Good-Feel has been the primary suspect for some time.
Given how much everyone assumed Good-Feel was behind Yoshi and the mysterious book, it makes all of Nintendo's secrecy surrounding the developers so silly. I will say that I hope this will not always be the case in the future, but I think we all know better than that.

Yoshi and the Mysterious Book Review – Like a good bedtime story
But even the best bedtime stories can get boring after you hear them enough times.