The game was first announced by Edmund McMillen and revealed a teaser logo from his The Binding of Isaac website on March 22, 2016 while The Binding of Isaac: Afterbirth † DLC's in development.
On March 31, Edmund leaked an image on Twitter featuring a fly and a hulking, grotesque-looking monster who is either a playable character or one of the bosses.
On April 6, Edmund leaked another image and confirms that there will be a teaser trailer video coming out some day. From this image, the game's graphics are cardboard styled with HUD textures similar from the core series of The Binding of Isaac. From the bottom of the screen, there is what appears to be an item inventory. A Dip and few Gaper enemies are also seen.
On April 8, James ID leaked an image on Twitter featuring three different-styled poop cardboards.
On April 13, on Twitter, James ID leaked another image featuring the poop monster clearly turns out to be the one who is previously leaked by Edmund back in March 31 from Twitter.
On April 19, from The Binding of Isaac website, with the following announcement of Afterbirth † DLC update, Edmund revealed an animated "game footage" image of the spin-off game, with the Beggar-like character (assumed to be Bum-bo) and Edmund's head in cardboard-styled graphics.
On May 10, again from The Binding of Isaac website, Edmund revealed a beta image, featuring two Flies and a Pooter during the fight.
On June 6, from The Binding of Isaac website, with the following announcement of a leaked Afterbirth † character, Edmund posted a image of the character Bumbo the Brave's cardboard profile, featuring the character's stats and powers.
On June 28, from The Binding of Isaac website, Edmund posted another image of the character's info. This time, it is Bumbo the Weird.
|The Binding of Isaac||Wrath of the Lamb • Eternal Edition|
|The Binding of Isaac: Rebirth||Afterbirth • Afterbirth † • Repentance|
|Other games||The Legend of Bum-bo • The Binding of Isaac: Four Souls|