He mentions it casually in the post, which is about upcoming booster content for The Binding of Isaac, referring to it as a “side note” and tacking the announcement onto the end of the post.
“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 dont want to spoil the fun yet but i can say this.
“its hard, its weird, its personal, it has amazing controls, its a totally new unannounced IP and its easily one of the largest games ive ever made level wise.” – Edmund McMillan on Tumblr
McMillan announced another new release last year, also via Tumblr – The Legend of Bumbo, a puzzle RPG. He then went on to tease yet another game, developed again with Tyler Glaiel, which has since been titled Øuroboros.
That game is a Mega Man-style platform shooter which features the main character from a previous game of his, Time Fcuk. Neither has yet been released.
Based on what McMillan has said, this newly announced game is clearly separate from either of those.
McMillan urges us to “stay tuned” for more information.