This guide will document tips, tricks, and best practices for getting these achievements.
Conditions for the achievements
What counts as "taking damage?"
- Getting hit by an enemy, enemy projectile, bomb
- Purchasing an item from the Devil Room.
- Spike door in the Curse Room.
What doesn't count as "taking damage?"
- Damage that is absorbed by shields, e.g. Holy Mantle or Infamy.
- Using the Blood Donation Machine or IV bag.
- Damage taken from the Devil Beggar.
- The "Bad Trip" or the "Health Down" pill effects.
- The Razor Blade and Blood Rights items.
- Using a "Health up!" pill.
- 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.
- 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 due to a bug.
Items to Get
- Skipping rooms: Most importantly IV The Emperor, then Crystal Ball, XXI The World and XIX The Sun, Dad's Key, The Compass and Treasure Map, and XRay Vision or Spelunker Hat for shortcuts
- Killing Mom or Mom's Heart: The Bible
- 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 for The Caves and The Depths, but not The Womb).
- Hitting Enemies through obstacles: Ouija Board, Brimstone, Ghost Baby, Mom's Knife
- Shielding: Halo Of Flies, Cube Of Meat, Guardian Angel, Sacrificial Dagger
- Temporary invincibility: Book Of Shadows, The Gamekid, My Little Unicorn, VII The Chariot to save you in a pinch
- Enemy Avoidance: Mom's Pad, Mom's Bra, The Hourglass, Mom's Contacts, Skatole against flies
- Self hitting: Blood Rights, Razor Blade and Kamikaze!
Items to Avoid
- Items that slow you down: Bucket of Lard, Odd Mushroom (Large),
- Items that can cause damage by accident: Anarchist Cookbook, Epic Fetus etc.
- Pills that might be 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 probably failed unless you took damage on another floor or they are soul hearts)
- Items that take effect when you're hurt: The Wafer, Habit, Dead Bird, The Black Bean, The Virus, Infestation. The Virus activates on contact with an enemy, so if you have a way to become invincible, such as the Book of the Shadows, The Virus can be used to deal damage without taking damage.The Virus also lowers speed, though not if you already have the same speed reduction from Odd Mushroom (Large).
Trinkets to Avoid
- Liberty Cap (chance of giving you the Odd Mushroom (Large) effect upon entering a room, which reduces speed. On the other hand it can give you the Compass effect, though)
- Bloody Penny (hearts are useless for you)
- Red Patch, Fish Head, Cursed Skull, A Missing Page, Umbilical Cord and The Polaroid (because they only work when damage is taken)
When Isaac carries the D6, his reroll ability can be extremely useful to get the certain items listed above that make the no damage runs easier. If you have not unlocked the D6, he is less advisable than ???, who has the same base stats. It may be worthwhile to try for these achievements in a challenge since a challenge will mean that you'll start with some strong items.
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 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.
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.
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 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.
- Use The Dice liberally - maximize the number of chances you get to use it. Aim for high priority items.
- Buy items from Devil Rooms in earlier floors, as the health will not be needed on later floors.
- Use bombs to escape a room that you don't think you can handle.
- Do not risk going over spikes.
- 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.
- Use items that hurt yourself (Blood Rights and Razor Blade), as they do not count as damage taken, and you will not use the health for something else
- It is possible to visit a Curse Room without taking damage, though it requires both a flying ability (which allows you to take no damage while entering) and an item that causes teleport, such as Teleport! or any Tarot Card that teleports to a specific room.
It is possible to fight in the Boss Room against the same boss multiple times, and thus obtain the no damage achievements easily by doing the following:
- After defeating a boss, spawn an enemy inside the room. There are multiple options on how to to this:
- 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.