Repentance introduced a "B-side" to every character in the game. Known as Tainted Characters, these are unlocked by reaching the "Home" stage. They aren't just palette swaps; they feature entirely different mechanics.
After over 6,000 reviews on Steam with a 96% positive rating, this is arguably the best value in roguelike gaming. While Hades has a better story and Dead Cells has better combat, Isaac has the most replayability .