The Legend of Bum-bo

The Legend of Bum-bo is a puzzle-based "deckbuilding roguelike" from Edmund McMillen (The Binding of Isaac, Super Meat Boy, The End Is Nigh), where players collect hoards of items that can be modified, upgraded and combined with others in many interesting ways. Play as one of many Bum-bo, each with its own unique abilities, as they smash, bash and splash their way through a variety of cardboard monstrosities, giant bosses and dark personal urges...
...oh, and it's also the prequel to The Binding of Isaac!