Wrath of the Lamb saw the addition of a new feature, challenges. Challenges are special playthroughs where the player starts with a specific item or setup, and some limitation such as no Treasure Rooms or the Curse of Darkness for every floor. Upon completion of each challenge, the player unlocks a new item that can be found in the game, as well as unlocking a Steam achievement. Completing challenges also counts as beating the game, so a new ending will be unlocked upon completion.
|Dark was the Night||
Gives you the Curse of Darkness.
You will have no map.
A glitch may occur when completing this challenge, giving you the achievement for completing the "7 Years Bad Luck" challenge but you still get the correct item. There is another glitch where it gives you neither.
|7 Years Bad Luck||
Starts you with minimum (negative) luck.
Increases your chances of getting a curse on any given floor.
Chance to not spawn a Treasure Room on floors.
You start without any activatable item.
When you complete this challenge, there is a bug that can make you get the achievement for completing the Challenge "Large Marge" (Challenge 3) instead of getting the achievement for Challenge 2 although you still get the item from completing Challenge 2.
Gives you the Curse of the Labyrinth. Treasure Rooms are present.
A glitch may occur when completing this challenge, giving you the achievement for completing the "Dark was the Night" challenge but you still get the correct item.
Beating the first boss in Necropolis XL instead of Mom will complete the challenge.
Gives you the Dead Cat item.
Treasure Rooms are present.
There are reports that players get the Guppy's Tail item without beating this challenge.
|Lord of the Flies||Gives you Infestation and The Mulligan. No Treasure Rooms.|
|The Doctor's Revenge!||Mom's Heart|
|Meat 4 Evar!||
Starts you with a level four Meat Boy. No Treasure Rooms.
It is possible to get two Meat Boys in this challenge as seen below.
|Spider Boy!||Gives you the Spider's Bite and the Mutant Spider. No Treasure Rooms.||
|Isaac Was Good Today||
Gives you the Holy Grail and The Halo. No Treasure Rooms. If you have not unlocked Sheol, even though you have been there with the devil trapdoor, you still can't complete the challenge. The chest will appear and you will have beaten Mom's Heart normally without completing the challenge.
You start without The Dice, even if you've unlocked it. No Treasure Rooms.
You do not need to complete all of the above challenges to unlock the Daddy Long Legs item, only The Purist challenge.
This challenge (initially locked), is unlocked by defeating Isaac in the Cathedral.
- You still can play the challenges as any character you want. When the screen starts fading to black, quickly press the "Esc" key to return to the main menu then the "Space" key to go back to the character selection screen, then just move to the character you want to play with (do not press "Space" to actually select that character, that will cancel the challenge and start a normal game). If done correctly, you can even play with characters that you haven't unlocked yet. Example, choosing Magdalene gives you four Heart Containers and the Yum Heart and Isaac's stats.. The exception to this is that selecting Isaac will not allow you to start with The Dice, even if you have already unlocked that item.
- Unlocking challenge-related achievements on Steam occasionally has some issues, usually resulting in two challenges having their corresponding achievements exchanged; For example, unlocking the Blue Candle achievement for completing "Large Marge". It is still apparently always possible to unlock all of the Steam achievements.
- However, if you do manage to unlock the wrong achievement, you can sometimes not receive the reward for a challenge because of it, due to it randomly deciding what achievement it unlocks (e.g., If you defeat "7 Years Bad Luck" but get the achievement for "Large Marge", everything is fine. However, beating "Large Marge" may result in it working correctly, so that you would get the right corresponding achievement, but since you already unlocked the achievement for "Large Marge", it will count as not being completed, so you will receive no item and the challenge will not be crossed out on the challenge page).
- When Challenge 1 ("Dark was the Night") is completed, you may not unlock the achievement but you can still find The Candle.
- It is possible to complete Challenge 10 ("The Purist") via Sheol instead of the Cathedral, if you are teleported to the I AM ERROR Room on The Womb 2. Inside is a single trap door which goes to Sheol; however, if you beat Satan, the challenge will be marked as completed.
- Getting the Curse of the Labyrinth on the goal level means that you only have to beat the first boss on the level to complete the challenge.
- Using the We Need to Go Deeper! item to pass by the floor of the boss triggering the success of a challenge will not trigger the challenge, nor the associated achievement.