The Binding of Isaac developer Edmund McMillen announced the contents of Isaac: Afterbirth Plus' second 'mod booster' pack yesterday, and right at the bottom of that blog post, as if to reward people for scrolling down, he revealed that he's been working on another project with frequent collaborator Tyler Glaiel. It's an "unannounced IP", so it's presumably got nothing to do with The Legend of Bum-bo, which was similarly teased last year, before retreating into the shadows, never to be whiffed again.
Here's what McMillen has to say about the secret project:
"On a side note not many of you know this but Tyler and I have been in crunch mode for the past 3 months trying to finish this secret project. We are coming close to announcing it and its release date, so keep and eye out for it, I don't want to spoil the fun yet but I can say this.
"It's hard, it's weird, it's personal, it has amazing controls, it's a totally new unannounced IP and it's easily one of the largest games I've ever made level wise."
I'm not going to speculate, because McMillen's announcements are always surprising, and because it sounds like we'll know before too long. So let's take a look at Afterbirth+ and its second mod booster pack, which once again incorporates some select mods into the base game. This time, give a big welcome to the projectile-repelling Telepathy, the item-ferrying Moving Box, the charge-replenishing Jumper Cables item and more.