According to Steam, I have sunk approximately 1,500 hours in The Binding of Isaac.1 Although I’m far from reaching a perfect savefile (often known as 1,000,000%) I can say with confidence that I have quite some knowledge on the game and its mechanics.

That’s why I was a bit disappointed while watching the otherwise excellent series Game Maker’s Toolkit, in particular the video How Games Do Health. In it, Mark Brown correctly identifies health as an important resource in TBoI, beyond its common mechanical role as the player’s general “allowance” for mistakes before the game is over—a role also identified by Arin “Egoraptor” Hanson in his Sequelitis episode Mega Man Classic vs. Mega Man X.

I watched the video and wished for Mark to make some kind of deep analysis on how Health in TBoI is used, because it’s not only non-obvious but also an important part of becoming a good TBoI player. Alas, GMTK is not a channel dedicated to analysis in single games2 and my ideas kept bubbling to the front of my mind. So, in accordance to Point 5 of The Cult of Done Manifesto, I’ll write this just to get it out of my mind and, hopefully, as an aid for any TBoI players, new and existing.

—Andy

A note on versions and spoilers

The vast majority of my experience is with the Nicalis version of the game—that is, The Binding of Isaac Rebirth/Afterbirth/Afterbirth+. Most of what I’m writing here should be applicable to the original Flash version, but I’m making no guarantees: it’s been at least 4 years since I last touched that version.

Also, for newbie players, there will be some spoilers for progress in this writeup. Even though TBoI is not lore-heavy, there are some mysteries to be found and I will be discussing them here, assuming you already know a bit about them. If you’re the kind of player that likes to figure out everything by yourself, this might spoil parts of the game for you.

You’ve been warned


Table of Contents


1 Health as Hit Points

In TBoI, just like in many other games, there are Health Points/Hit Points, representing the player’s general health and ability to continue on—a remnant from roleplaying gamess. TBoI borrows many design elements from The Legend of Zelda, health being only one of those: Isaac starts3 with three hearts and takes half a heart of damage per hit taken. When there are no more hearts, the game is over.

So far, so good. Normal videogame health. However, special mechanics start right here. In particular, a good TBoI player should know how health works in TBoI and, much more importantly, how to use health effectively.

Special Case 1: Bosses, champions and the second half of the game
Almost all Bosses’ attacks deal one full heart of damage. There are also champion enemies, which are “amped-up” versions of regular enemies in one way or another (extra health, extra attacks, explosive death, etc.) Champion enemies also deal 1 full heart of damage per attack
Also, from floor 7 (Womb 1) onwards4, all regular attacks deal one full heart of damage.

There are also other ways of getting damaged that are not enemies:

Special Case 2: Environmental damage
The main sources of environmental damage are spikes on the floor and fireplaces of different colors. Stepping on either of these will result in a full heart of damage

It’s worth noting that, just like in TLoZ, your maximum HP is determined by how many Heart containers you have. Once you’ve reached this maximum, you cannot pick up additional hearts unless they are empty (that is, after you’ve taken damage. In general, you can gain extra heart containers by obtaining an “HP-up” pickup item like the following

Magic Mushroom <3 Raw Liver (+2 HP)
Lunch Dinner 5 Dessert 6
Breakfast Rotten Meat Super Bandage
The Halo Blood Bag Odd Mushroom (thick/fat version)
Bucket of Lard (+2 HP) Stigmata Stem Cells
Sacred Heart Holy Grail Super Meat Boy Super Fan
Meat! Placenta Old Bandage (only gives you an empty heart container)
Black Lotus Magic Scab Capricorn
Maggy’s Bow Thunder Thighs The Body (+3 HP)
Blue Cap Crack Jacks Moldy Bread

Several of these also come with one or more additional changes, but for the purposes of this guide I will not list them all. See the references for more information.


2 Other sources of health

2.1 Soul hearts and Demon hearts

Your regular hearts aren’t the only source of health in TBoI. There are two main exceptions:

Special Case 3: Soul hearts
Soul hearts are grey-colored hearts that function almost exactly the same as regular hearts, with two important distinctions 1. Soul hearts always stack on top of your existing hearts (which means that they will “get hit” before your red hearts, and 2. Soul hearts are temporary: once they’re gone, they’re gone; unlike your regular heart containers that stay even if you suffer damage

Soul hearts can drop from a regular room fight, as a reward for defeating some champions. They are also granted upon pick up of the following items (note that some of these also appear in the previous table, this is no mistake)

Rosary Book of Revelations The Mark
The Pact Super Bandage Scapular
Squeezy Black Lotus Cancer
The Mind Latch Key Crown of Light
PJs Binky Metal Plate
Cone Head Glyph of Balance Bozo
Blanket

The following items may also give you soul hearts:

  • The Nail—upon use
  • The Relic—gives a soul heart every 4 rooms
  • Guppy’s Paw—upon use converts 1 heart container to 3 soul hearts. This can be done any number of times while you have heart containers
  • Crystal Ball—sometimes, upon use
  • Pandora’s Box—Only if used on the very first floor (Basement 1), the third floor (Caves 1) or the fifth floor (Depths 1)
  • Sharp Straw—upon use has a chance to drop 1/2 a soul heart
  • Death’s List—if all enemies in a room are killed in a particular order, it may drop a soul heart
  • Dark Bum—has a chance to give you a soul heart if you let him consume red hearts
  • Gimpy—has a chance to drop a soul heart upon taking damage
Special Case 4: Demon hearts
Demon hearts are black-colored hearts that function almost exactly like soul hearts, with the added benefit that upon disappearance you deal 400 “unblockable” damage to every enemy in the room

Demon hearts can come from the following items:

Ceremonial Robes Black Lotus Black Candle
Missing Page 2 Safety Pin Match Book
Empty Vessel

The following items may also give you demon hearts:

  • Abaddon—upon pickup, removes all heart containers and gives you 6 black hearts
  • The Satanic Bible—upon use
  • Dark Bum—has a chance to give you a demon heart if you let him consume red hearts
  • Gimpy—has a chance to drop a demon heart upon taking damage
  • Pandora’s Box—Only if used on Sheol
  • Maw of the Void—After holding fire for 3 seconds and releasing, it will create a black ring around Isaac that damages enemies. When defeated by this ring, enemies have a chance of dropping a demon heart
  • Athame—Similar to Maw of the Void, but the black ring will only trigger upon taking damage
  • Sacrificial Altar–upon use, only if you sacrifice either the Guardian Angel, Sworn Protector or Seraphim

2.1.1 Why should I care for Soul/Demon hearts?

Newbie TBoI players tend to value red hearts and heart containers as more important than Soul/Demon hearts—after all, the latter cannot be regenerated and many have been trained for years to see health as one of the most important aspects of gameplay.

But one of the major points of this guide is to teach those players that a sufficiently skilled TBoI player will often value Soul/Demon hearts above regular HP. Why, just this morning I saw episode 1302 of Ryan “Northernlion” Letorneau playing the game and passing over an HP upgrade just one room before the Final Boss. Why?

2.2 Eternal hearts and Bone hearts

Although not as important, Eternal hearts and Bone hearts are also sources of Hit Points and have their own use cases. The reason for separating these from the Soul and Demon hearts is that those are mechanically much more important for the aspiring TBoI Platinum God.

Special case 5: Eternal hearts
Eternal hearts are white-colored half-hearts. They always sit on top of your last red heart but before any soul or demon hearts. This means that after all soul or demon hearts are exhausted, the first hit you receive will hit the eternal heart.

Eternal hearts are a special source of HP: If you manage to get two of them in the same floor—or if you take one to the next floor—you will get an extra heart container.
Special case 6: Bone hearts
Bone hearts are bone-looking hearts that can hold a regular red heart inside them, acting as a sort of “shell”. An empty bone heart will resist a single hit of damage and will disappear afterwards. This also means that a full bone heart will sustain 3 hits.

Bone hearts act like a temporary heart container: a bone heart only disappears once it’s empty AND receives damage.

Due to their color and the mechanical differences, it’s common to refer to regular hearts as “red HP”. This is a crucial difference that will be discussed later in this guide.


3 Health as a test of skill

TBoI uses health as a test of skill in a very interesting way.

Starting from floor 2 (Basement 2) and until floor 8 (Womb 2) you start each floor with a nonzero chance of getting a Devil Room after defeating the floor’s Boss.7 This chance is relatively high (from 33.75% up to 100%) until you get damaged. Then it’s drastically reduced down to a 0.25% to 9% chance.

OK, it’s more complicated than that.

Your chances for getting a Devil Room are only reduced if you receive red heart damage. What this means is that the first purpose of Soul/Demon hearts is now evident: they effectively serve as a shield for your red hearts so that you can get to the Devil Room safely. No extra hearts means you need te be extra careful to not take any damage in during the whole floor.

If this sounds daunting is because it’s designed that way. This is similar to many other games, most notably the Dark Souls series: the game rewards knowing your enemies and their attack patterns, having good situational awareness and prioritizing some enemies above others.

Also, as the game progresses, the game’s difficulty goes up. In order to maintain your odds of getting a Devil Room you need to step up not only your own abilities as a player, but also your character’s general prowess (speed, damage, fire rate, etc.) This too requires knowledge of the game and its items: some items are just not worth it and some are useful only in very specific circumstances8.


4 Health as a Risk/Reward mechanism

So you might be wondering «What the hell is a Devil Room, then?». Simply put, is a way to obtain some pretty powerful items, some of which are (or can become) downright broken.9

You go through a single floor without sustaining red heart damage and a mysterious door opens in the room.10 In it, you’ll find a Baphomet sculpture and a choice of two to four items11, laid out like they do in the Shop. Only, instead of regular prices, the items show you one or two hearts.12

Let’s restate this: Devil Room items cost you your life. A literal Faustian bargain: power at the cost of reduced health and (as discussed) reduced ability to make mistakes.

While this might seem like an option that careful players might want to avoid, the game makes sure you think twice. As discussed above, the power level of the enemies tends upwards and if you don’t meet or surpass their might, your run may as well be doomed. Sure, skilled players can defeat the game without intervention from Below (or Above) but this is rarely the case.

So what seems like a simple risk/reward mechanism is actually the regular gameplay loop for progression. Who said health is a simplistic game element?


5 Health as an exchange currency

Health in general is also a way to obtain something money or even items, if you’re willing to risk losing life in these cases.

Special Case 7: Blood donation machine
Upon touching the blood donation machine, Isaac wil suffer 1/2 or 1 heart of damage, depending on the floor depth (see Special case 1) and will spawn 1 to 3 coins. Every donation also has a chance of exploding the machine, at which point it will spawn either the Blood Bag or the IV Bag items
Special Case 8: Devil beggars
Upon touching the Devil beggar, Isaac will suffer 1/2 or 1 heart of damage, depending on the floor depth. Every donation has a chance of spawning useful pickups13 or an item from the Devil Room
Special Case 9: Guppy’s Tail
Upon use, Guppy’s Tail will take away one heart container and give Isaac three Soul hearts. Has no effect if you have no red hearts
Special Case 10: Potato peeler
Upon use, it will remove one heart container and Isaac wil gain both a damage bonus and one copy of the item Cube of Meat. Has no effect if you have no red hearts

Although not exactly the same as the deals with the Devil, these cases are a way to not only obtain money and pickups, but also a safe way to get your health down to 1 or less red hearts. Why this is important will be covered in a later section.

It’s also worth noting that having multiple Cubes of Meat is an interesting tradeoff:

  1. Having one will give Isaac a literal cube of meat that orbits Isaac, blocks enemy bullets and makes contact damage.
  2. Having two is the same, but the Cube now occasionally shoots a bullet in the same direction as Isaac
  3. Having three or four will detach the cube and will transform it into a Super Meat Boy-like being that chases down enemies on its own and deals contact damage.
  4. Having more copies starts the cycle again (but you retain all previously gained Cubes)
Special Case 11: Blood Rights
Upon use, Blood Rights will deal one full heart of damage to Isaac and 40 unblockable damage to every enemy in the room.

6 Health as a marker of ‘run health’

I don’t know how best to express this, but TBoI also treats your health as a general indicator of how well your run is doing.

This is most evident in two special rooms: Challenge Rooms and Boss Challenge Rooms

6.1 Challenge Rooms

This kind of room has some treasure inside that, on pickup, will trigger 3 waves of enemies, one after the other. While none of them are particularly dangerous14, you can’t exit the room until you kill all the waves or teleport away.

These rooms aren’t always open, though. You must have full HP in order to open them. Well, kind of.

Special Case 12: Challenge Rooms
Challenge rooms are open only when your total combined health (including Soul/Demon hearts) is at equal or greater than your heart containers.

For example, consider having a single red heart, two empty heart containers and three demon hearts: 💖💔💔🖤🖤🖤 This is enough to open the Challenge Room, since you have a total of 4 hearts and 3 heart containers.

In other words, Challenge rooms require that you be «at full health» or equivalent in order to tackle them.

6.2 Boss Challenge Rooms

Like regular Challenge Rooms, but this tends to have better rewards, but instead of three waves of enemies, you get to fight two rounds of bosses, one after another15.

Like regular Challenge Rooms, these are open only on a specific circumstance.

Special Case 13: Boss Challenge Rooms
Boss Challenge Rooms are open only when you have one or less red hearts

Again, this takes into account your red hearts, not your heart containers. And yes, you can have zero heart containers and it’s often a good strategy to have this little HP!

Observant readers will note that, unlike regular Challenge Rooms, these require that you be «near death» or equivalent in order to tackle them.


7 Health management or why having 1 HP is near-optimal

New TBoI players, as mentioned above, tend to overrate HP, prioritizing it above other more important stats.16 Newbie TBoI players might be wondering about the title of this section and why I believe it to be so (along with many other more skilled players).

In short, you can apply the Magic: the Gathering maxim here: The only hit point that matters is the last one

7.1 How to open Challenge Rooms

Astute readers might have realized this by now, but the conditions for opening Regular Challenge Rooms and Boss Challenge Rooms are not mutually exclusive. Having exactly one or zero heart containers means you can fulfill both conditions at the same time and in doing so, increasing your chances for getting something good out of those rooms.

7.2 Outsmarting the Devil

It’s true that some items in the Devil Room cost you 1 heart, and some cost you 2. What the game never tells you is that there is a way to get more bang for your heart in these deals with the Devil.

Special Case 14: 2-heart deals with the Devil
It is possible to buy a 2-heart item in the Devil Room if you have only 1 heart container. It will only take away the one heart container

Sweet! This is why it’s important to bear in mind that the deals with the Devil have to be made in a specific order.17 With only 2 HP you can get both Ceremonial Robes and Brimstone, but only if you get them in that order.

But you have to be careful here as well. Deals with the Devil are also possible with zero heart containers, but in this case you get the short end of the deal.

Special Case 15: Deals with the Devil without heart containers
When you have zero heart containers, all Devil Room items cost you three Soul/Demon hearts.

This is awful. From a damage perspective, red hearts and Soul hearts are functionally the same, but if you don’t have any HP, all of these powerful items are 150-300% their original cost! Sometimes this cost is worth it, but it’s always preferable to pay less for exactly the same item.

There are also other ways of creatively using your health in Deals with the Devil

Special Case 16: Respawning as Dark Judas or «???»
The Devil Room items Judas’ Shadow and Ankh both give you an extra life. The trick is that they also respawn you with zero heart containers. For Judas’ Shadow you respawn with 2 black hearts and have the ability to gain further heart containers later in the run. With the Ankh you respawn with three Soul hearts and can no longer gain heart containers, gaining instead one Soul heart instead.
Special Case 17: Not today, Satan!
Some items in Devil Rooms give you Soul/Demon hearts immediately after pickup. These items are: The Mark, The Pact, Ceremonial Robes, Abaddon, Missing Page 2 and Empty Vessel

These items can be bought on your last heart container but since they give you extra hearts immediately, you won’t be killed for trading up your last heart.

Special Case 18: Dead Cat
Upon pickup, the item Dead Cat will set your heart containers to 1 and give you 9 extra lives, with the caveat that every time you respawn you only respawn with one heart container

The condition of setting your heart containers back to 1 might suck for some, but it’s also a way of cheating the Devil. Note that this item doesn’t reduce your heart containers, it just sets them to 1. This means that you can go into a Devil Room with only 1 heart container and buy 2 items with it. You just need to buy first the Dead Cat, then your HP is set back to 1 and you can buy the other item with exactly 1 heart! Even if this kills you, you still have 8 more lives ahead of you.

7.3 Life with one or less HP

We’ve seen how having exactly one heart container is useful for both Challenge Rooms and Devil Rooms, but there’s more about having one or zero heart containers.

Special Case 19: Dark Prince’s Crown
The item Dark Prince’s Crown gives you a passive bonus to range, fire rate and shot speed while you have exactly 1 red heart
Special Case 20: Whore of Babylon
The item Whore of Babylon grants you a passive bonus to damage and speed while you have 1/2 or less red hearts
Special case 21: Empty Vessel
The item Empty Vessel grants you flight and an occasional shield if you have zero heart containers

These three items are all about getting bonuses while on «low HP». There’s opinions on which of these is better, but I won’t pronounce them. I only present these as further examples of why having low Red Containers can be a good idea.

Special Case 22: Polaroid and The Negative
After unlocking them, Polaroid and The Negative drop after defeating Mom and taking one makes the other disappear. If Isaac gets hit while having 1/2 or less red hearts Polaroid will deploy a shield for a few seconds, and The Negative will deal damage to all enemies in the room

In order to get to the later levels (Chest/Dark Room) you need to take one of these. They both provide bonuses when hit at «low HP».


8 Conclusions

Health is extremely important in The Binding of Isaac, and not only because once it runs out you go back to the beginning in true roguelike fashion. Learning how to manage and use health to your advantage is a skill in TBoI much like dodging, and recognizing patterns. The aspiring player should learn these cases little by little in order to improve themselves over time.

Also, the aspiring game designer should, in my humble opinion, look up to this game to learn a trick or two on how to use health (or other resources) in their game. The complexity of this system is only a small part of why, almost a decade after its release, the game still sees love from both the developer and its players.

9 Version history

  • 1.00; 2019-07-14

    First version, to be pubished on Everything2.



  1. Combined in its original Flash format and the re-release The Binding of Isaac Afterbirth+↩︎

  2. Well, not generally↩︎

  3. I will be using Isaac and not the other characters as a basis for comparison. The differences will become evident as the guide progresses↩︎

  4. Yes, beating Mom is barely the beginning of the real game.↩︎

  5. Actually a can of Dog food↩︎

  6. Actually a bag of Dog food↩︎

  7. Technically, you can get to the Devil Room in all floors with a lucky Red Chest or via the use of the Joker card, but those have nothing to do with the actual Health management that is the focus of this guide↩︎

  8. For instance the item Soy Milk. It’s a terrible item to have because it drastically lowers your damage while turning your fire rate up to eleven. But if you manage to have both Soy Milk and Libra (which “balances” all your stats) you end up with a decent fire rate and damage, good enough for almost all floors.↩︎

  9. in my opinion, the Devil Room items actually are the most powerful items in the game. While Angel Room items are statistically more powerful, even getting to one is more unreliable, and the chances of an Angel Room actually having, say, Godhead, are so low that they are not useful planning around. I’d rather have a less powerful but more reliable set of items.↩︎

  10. I don’t recall right now, but there’s only a few rooms where the chance for a Devil Room is actually 100%, most notably the second floor (Basement 2). I’m overlooking the actual chances for now.↩︎

  11. This is not guaranteed: some Devil rooms may not have items, but red chests or a surprise fight with Krampus. I’m also glossing over this detail.↩︎

  12. Or three soul hearts, but this will be discussed later.↩︎

  13. Either cards, pills or trinkets↩︎

  14. compared to the floor’s power level, that is.↩︎

  15. Observant players will note that it’s not necessarily two bosses, but two rounds. You might have the bad luck of having the pink variant of Monstro, which always spawns in pairs and sometimes in fours.↩︎

  16. Namely: damage and fire rate. Speed and range as well, but on a secondary plane.↩︎

  17. I never thought I would type out that phrase in my life.↩︎

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