The Binding of Isaac: Afterbirth is the first DLC for The Binding of Isaac: Rebirth, released on October 30 2015 with new Greed Mode, a new final area with a new final boss, Daily Runs, 120 new items, and more.
Blue Womb: A new area, featuring a new ending and final boss.
Daily Runs: Daily seeded runs with online leaderboards.
Two new characters, Lilith and Keeper.
10 new challenges.
4 new alternate chapters: Burning Basement, Flooded Caves, Dank Depths, and Scarred Womb.
Many new room layouts including tiny rooms, long hallways, and L-shaped rooms.
New room types like trap rooms, double treasure rooms, and closets.
New special seeds, along with a seed code combo page.
An expanded soundtrack.
An extra HUD option, allowing items picked up to be displayed on-screen.
9 new transformations.
New bosses, along with new variations of bosses introduced in Rebirth.
Updated item combo system.
New co-op babies.
An improved collection page that shows item descriptions.