Some of the most difficult achievements in the game are the "no damage" achievements - Basement Boy, Spelunker Boy, Dark Boy, and Mamas Boy. They are unlocked by completing The Basement, The Caves, The Depths, or The Womb without taking damage, respectively. There is no achievement for completing Sheol, the Cathedral or The Chest this way.

This guide will document tips, tricks, and best practices for getting these achievements.

Contents 1 Conditions for achieving the achievements 1.1 What counts as "taking damage?" 1.2 What doesn't count as "taking damage?" 1.3 What are the other caveats? 1.4 Other information 2 Items 2.1 Items to Get 2.2 Items to Avoid 2.3 Items to Ignore/Reroll 2.4 Trinkets to Avoid 2.5 Why these items? 3 Characters 3.1 Isaac 3.2 Magdalene 3.3 Cain 3.4 Judas 3.5 Eve 3.6 ??? 3.7 Samson 4 General Strategies 5 Using Challenges 6 "Special" Strategies

Conditions for achieving the achievements

What counts as "taking damage?"

• Getting hit by an enemy, enemy projectile, bomb (pretty much what you would expect)
• Purchasing an item from the Devil Room.

What doesn't count as "taking damage?"

• Using the Blood Donation Machine or IV bag.
• Damage taken from the Devil Beggar.
• The "Bad Trip" or the "Health Down" Pill effect.
• The Kamikaze!, Razor Blade, and Blood Rights items.
• Using a "Health up!" pill.

What are the other caveats?

• You cannot use We Need To Go Deeper! or the I AM ERROR room to avoid the second level boss of the area.
• You cannot use Forget Me Now to reset the second level of an area.
• Dying while having items like 1UP, Dead Cat or the Ankh will not reset the damage status for the level.

Other information

• Taking damage in an area will not disable all the boy achievements, only the one applicable to the current area. (you can take damage in the Basement and still unlock Spelunker in the Caves)
• The achievement unlocks when you defeat the second boss, meaning that you can explore the rest of the level or enter the devil room afterwards.
• In order to get the achievement, you only need to beat two bosses from the current chapter. You will also get the achievement if you defeat two floor bosses in the same floor. Note that bosses outside of the Boss Room are not considered to be floor bosses.
• Using Forget Me Now will reset the damage status for the current level.
• If you have Wrath of the Lamb, you can use challenges to get the achievements.
• If you have Wrath of the Lamb, killing Mom while under the foot's shadow will cause explosion damage.

Items

Items to Get

1. Skipping rooms: Most importantly IV The Emperor, then Crystal Ball, XXI The World and XIX The Sun, The Compass and Treasure Map, and XRay Vision or Spelunker Hat for shortcuts
2. Killing Mom or Mom's Heart: The Bible
3. Flight: Transcendence, Lord Of The Pit, A Pony, (Dead Dove, Spirit Of The Night) - WotL DLC. (If you can't find any of these, The Ladder is almost as good).
4. Hitting Enemies through obstacles: Ouija Board, Brimstone, Ghost Baby
5. Shielding: Halo Of Flies, Cube Of Meat, Guardian Angel
6. Temporary invicibility: Book Of Shadows, The Gamekid, My Little Unicorn, VII The Chariot to save you in a pinch
7. Enemy Avoidance: Mom's Pad, Mom's Bra, The Hourglass, Mom's Contacts, Skatole against flies

Items to Avoid

• Items that slow you down: Bucket of Lard, Odd Mushroom (Large),
• Items that can cause damage: Anarchist Cookbook, etc.
• Pills that might be Health Up (or Health Down if you only have one heart container), or Telepills on the 2nd level of the area (can bring you to I AM ERROR, which forces you to skip the 2nd boss.
  TIP:You can identify pills safely after you've killed the 2nd level's boss)
• The Book of Revelations (in the Womb I, since you'll get Death, and you don't need the soul hearts anyway)

Items to Ignore/Reroll

• Items that give hearts of any kind (if you need them, you failed)
• Items that take effect when you're hurt The Wafer, Habit, Dead Bird, The Black Bean

Trinkets to Avoid

• Liberty Cap (chance of giving you the Odd Mushroom (Large) effect upon entering a room. On the other hand it can give you the Compass effect, though)
• Bloody Penny (red hearts are useless for you)
• Child's Heart (same reason)
• Red Patch (because it only works when damage is taken)

Why these items?

Your number one priority is avoiding damage.

This is why Transcendence and other flight items are so important. There are rooms you may stumble across that place you directly in front of an enemy with no means of escape. Being able to move over pits and rocks is a huge advantage in this regard.

This is also why protective items such as the Halo of Flies are important - they will block many incoming enemy projectiles you might not be able to avoid.

With a "flying" item and an attack that goes through obstacles, you can hover over a rock and attack enemies without them being able to harm you.

Characters

Isaac

When Isaac carries the D6, his reroll ability can be extremely useful to get the certain items listed above that make the iron man runs easier for you. If you have not unlocked the D6, he is less advisable than ???, who has the same base stats. (See below).

Magdalene

Magdalene's great amount of health and her Yum Heart won't help you for your goal. In addition, she has a very low base speed, which makes dodging attacks or evading enemies that run into you very hard. Her only upside might be the possibility of excessive deals with the devil in the early levels before trying the Dark Boy or Mamas Boy, but usually this will merely just get her stats on the same level as other characters. Remember: Deals with the Devil count as damage, so you can't do them in the "no damage area". Overall, she is the least advisable for no damage runs.

Cain

Cain has a considerable base damage of 3, as well as a high base speed, and his Lucky Foot  makes gambling in the arcade very profitable, but he is more likely to get Health Up Pills, which count as damage.FIXED AS OF 1.48

Judas

Judas is very advisable simply because of his high damage output (base damage of 4, Book of Belial). Dealing more damage means clearing rooms faster and thus having a shorter period of time being exposed to danger. His low health is not a drawback, since your goal is to not take any hits in the first place.

Eve

While Eve seems like an awful choice since she is a character intended to get better by self-inflicting damage, getting and keeping her to the powerful demon state through Whore of Babylon can still makes her a moderate choice. She also has one the highest base speeds, which helps you dodge attacks.

???

??? has some advantages over other characters when picking up certain items. Whore of Babylon will permanently turn him into the Demon state. Again, since you are attempting no damage runs, his inability to recover health normally is not a drawback in this case.

Samson

Samson is less advisable, but still a considerable choice, since Blood Lust can help clear rooms with many enemies more easily, which are the hardest to clear without taking damage.

General Strategies

• Use The Dice liberally - maximize the number of chances you get to use it. Aim for high priority items. Hang on to The Dice for as long as you can.
• Buy items from Devil Rooms in earlier floors. Remember, you won't need the extra health on late floors!
• Become comfortable with enemy movement patterns. Don't panic! Avoid any enemies first, and then start attacking them.
• Avoid Gauntlets unless you're familiar with the enemies that will spawn and there is a gold chest or compass inside.
• Avoid Devil Rooms when trying not to take damage. Deals with the Devil count as damage taken, and the Lump of Coal isn't worth fighting Krampus.
• Use The Emperor Tarot Card to teleport to the level boss if you can handle it.
• Use bombs to escape a room that you don't think you can handle.
• Do not risk going over spikes.
• Be prepared to restart the game if you take damage.
• Don't be greedy and postpone the fight if you think you can take on the boss without the extra items you might get by visiting the rest of the level.
• In Wrath of the Lamb, an easy way of achieving Dark Boy/Mama's Boy is to obtain The Bible whilst holding IV The Emperor. In combination, these allow you to skip the final floor of the Depths/Womb entirely. This combination is a lot more effective if your current floor is affected by the Curse of the Labyrinth.

Using Challenges

Becasuse it will also earn the no damage archievemetns, in Wrath of the Lamb it is also possible to use challenges to provide powerful usefull starting items.

There's also another advantage : As there aren't any treasure rooms (which is kind of balanced out by a set of starting items), one can focus on clearing the whole stage more quickly, therefore reducing the risks of taking damage.

The following challenges provise good item loadouts.

• The Doctor's Revenge! : Dr. Fetus
• Meat 4 Evar! :Level 4 Cube Of Meat
• Spider Boy! : Mutant Spider & Spider's Bite
• Isaac Was Good Today : Holy Grail & The Halo

"Special" Strategies

It is possible to fight in the Boss Room against the same boss multiple times by doing the following:

• After deafeating a boss, spawn an enemy inside the room. There are multiple options on how to to this:
  • Spawn a Fly by using aPortable Slot or Slot Machine (created with aWheel of Fortune Tarot card)
  • Spawn a Spider by killing a Demon Beggar with a Bomb (the beggar has a chance to appear when Judgement Tarot card is used)
• Leave the Boss Room
• Enter the Boss Room again. Since the game will register enemies left in the boss room as an unfinished boss fight, you will fight the same boss (or an alternative version of it) again.
• Since you beat two bosses from the same chapter, the game will count that chapter as beaten and you get the corresponding achievement.