Edmund McMillen and Florian Himsl's indie PC game The Binding of Isaac has done quite well for itself since it launched last fall. The $5 game, which plays like a mash-up of The Legend of Zelda and a roguelike, launched on Steam originally and was quickly pegged as a likely multiplatform port. Next up for Isaac, however, is an expansion pack, as confirmed by McMillen on Twitter.

The Wrath of the Lamb expansion will add "at least 50% more than what is already in [the] game," he wrote in reply to one user's Formspring query. McMillen also confirmed that composer Danny Baranowsky will be lending at least five new music tracks to the game.

He later told Joystiq in an e-mail exchange that Wrath is coming in "the next 2-4 months," and that the possible Nintendo 3DS port that's been discussed will pack in the expansion, assuming the release happens. Finally, McMillen revealed that this will be the only Lamb expansion we'll be seeing, since he'll have "nothing else" to add once Wrath is completed.

Source: Twitter, Joystiq