Against all odds (and taste), a Flash game about naked children violently crying on monsters made out of poop, piss and blood was (and still is) one of the most enduring successes of the action roguelike boom. Eleven years, one reboot and four expansions later, The Binding Of Isaac remains hugely popular. After a long period lying fallow, 2021’s Repentance expansion (based on community mega-mod Antibirth) brought new life to the game, almost doubling its size and giving players hundreds of new goals to chase after and secrets to uncover.
Seeing fan-made content elevated to an official expansion lit a fire under the modding community. They’ve been hard at work, and now the fans have rolled out the first true expansion-scale mod for Repentance. It’s a great excuse to revisit the game, and also gives new players a jumping-on point and an introduction to modding this grisly dungeon crawl.
Install this one
What's the best version of The Binding of Isaac?
Just to be confusing, there are two completely separate versions of The Binding Of Isaac, each with their own expansions: The original Flash-based 2011 version and the 2014 ‘Rebirth’ version running on its own bespoke engine. For the biggest and best experience, you’ll want the Rebirth Complete Bundle on Steam, which includes the newer base game and all three expansions, clocking in at a hefty $51 when not on sale. It’s not cheap, but it’s also a game you can play for hundreds of hours without seeing everything.
Sadly, there’s no bargain basement upgrade option if you own the original 2011 version of the game. You’re just going to have to buy the whole basement again. While the game is also available on GOG, I highly recommend the Steam version for modding ease-of-use.
First steps
Lie down, try not to cry, cry a lot
For new players, the best thing to do is just jump into the game blind and get the fear of death beat out of you—you will be dying often, and that’s fine. If you’re on a completely fresh save, it’ll even show you some mercy, giving you a shortened version of the dungeon with a more controlled pool of items, bosses and enemies to deal with. Your first couple tries should just be focused on learning the ropes and defeating Isaac’s mom for the first time.
Once that’s done, the game truly begins, unfolding into a thorny, death-filled puzzle box. Almost every run from here on out is going to unlock new stuff. Some of it dangerous, some of it useful, all of it shuffled into a growing bestiary of random spawn and drop lists. The more you play, the more chaotic and uncontrollable the game becomes. Half the game is learning to roll with the punches, and learning what familiar item combos work best.
There is a true and definitive ending laying at the end of a lot of secrets, unlocks, a reversed run through the dungeon and a boss gauntlet, but that’s just where the story wraps up. Then you unlock the Tainted characters; a full set of more advanced sad naked children to throw into the basement. Truly, Isaac is the gift that keeps on giving.
For returning players, unless you’re a veteran with this game burnt inexorably into your muscle memory, consider starting a fresh save. It’ll be a long march to unlock everything again, admittedly, but if you’ve missed out on an expansion or three, you may appreciate a slower ramp-up.
Once you’re familiarized and up to speed, oh, there’s so many options. I’ve hand-picked a selection of the amazing mods available for the latest version of Isaac. Give them all a try: It’s surprising how high you can stack that house of cards before it all comes tumbling down.
Modding prerequisites
Insulate your Hell Basement
Here’s a few bits and pieces from the Steam Workshop that you should have installed by default, as they ensure that everything else plays nice.
Custom Stage API by Filloax, budjmt & Deadinfinity won’t do anything directly, but it is a requirement of several larger mods. Best grab it first.
Mod Config Menu - Continued by Chifilly is another prerequisite. Many mods offer additional customization options. This lets you access them all from a single handy panel, accessible by pressing L or F10. Some of the mods below also have control panels of their own activated by pressing C or F1, although this can be rebound.
Mod Compatibility Hack by melon & Deadinfinity hammers out some underlying issues with the mod system, and helps retain unlocks in mods that you might have uninstalled and then reinstalled at a later date.
MiniMAPI by Wofsauge and Taz is another prerequisite for some more elaborate mods, but adds some extra quality-of-life features, including more map icon types and minimap resizing.
Save File Crash Fix by kittenchilly ensures that your game won’t crash if you start the game with a save file containing a character that (for whatever reason) no longer exists. You might not even need it, but it’s good to have.
Quality of life & Cosmetic mods
For a cozier cellar
Once upon a time, Issac’s adventure was relatively straightforward. One remake and four expansions later and it is an almost incomprehensibly complex web of systems and synergies. Here’s a few mods to make all that easier to wrap your noodle around, and a few just to make things a little prettier.
External Item Descriptions by Wolfsauge and fly_6 is incredibly handy. Compatible with most mods that add items, this tells you what each new piece of gear is going to do before you pick it up. You can also hold your map button to check what your carried trinkets, cards and pills (if identified) will do. Invaluable for those with bad memories. Like me.
Encyclopedia by ryon and AgentCucco removes the need for you to have a wiki page open at all times while playing, and just lets you browse an in-game library of useful info. It requires External Item Descriptions for many features, so get that too.
GoodTrip by Tarako lets you teleport directly from any cleared room to any that you’d previously completed—a familiar feature for Enter The Gungeon players. This mod could be considered cheating, as it’ll make hitting timer-based goals easier, but that’s for you to decide. If you want to use the mouse to click on the teleport map in fullscreen mode, see the tips section below.
Visible Challenge Unlocks by Akeldama doesn’t have broad mod compatibility, but it’s great for mostly-vanilla players hunting for specific unlocks. It’ll tell you what beating each challenge will reward you with. Simple and handy.
Enhanced Boss Bars by Wofsauge and Blind, The Bound Demon adds a little visual flair to Isaac’s bigger battles—unique boss health bar art for every major fight. Most good mods that add new bosses also support this.
Gameplay mods
Subterranean mod cons
Arcade Cabinets by HabosBabaFos, Thicco Catto and chug all this is a humble name for a stunning little mod. It adds playable arcade machines to the arcade room. Eight of them, each being an 8-bit styled minigame with its own art, sound, mechanics and music. It costs five cents to play, and of course there’s some fun rewards to be earned. It should be compatible with most mods, but runs the largest risk of breaking with custom characters.
Heaven’s Call by Ultrinik adds the Astral Challenge Room, a new chamber type containing Zodiac-themed items, plus new boss fights against planetary-themed opponents. This being The Binding Of Isaac, only the four gas giants are represented right now, and of course Uranus is the least classy of them. More are planned, but this set is all fun and tough encounters.
Epiphany (by a large team—see the Workshop page) is a great pick for the three of you who think Isaac doesn’t have enough playable characters in Repentance. On top of the unlockable Tainted variants, this mod aims to add extra technical ‘Tarnished’ versions of all 17 characters, each with their own special unlock requirements and personal items to collect. So far, only six are complete, but they’re an impressive set, and this mod is designed to be compatible with Fiend Folio below.
Da Rules by JSG is the mod for anyone tired of the (item) grind who just wants to play with Isaac’s huge toybox of loot and monsters. While not quite as powerful as delving into the mod API, this gives you a huge amount of freedom to tweak and tune the game, and add custom modifiers to the experience.
Overhauls & Expansions
Does a sub-basement imply a dom basement?
Fiend Folio Reheated is the key reason why so many people are getting into modding Isaac right now. First released for the Afterbirth+ expansion, but recently expanded and re-launched for Repentance, Fiend Folio is a colossal community collaboration (the work of over 40 modders) adding over 500 new monsters, 23 new bosses, 140+ new items, two new playable characters, 10 challenges and literally tens of thousands of new room layouts. Add that to the already massive random spawn lists in the game and you’re unlikely to see much repetition for a while.
While that could be a recipe for disaster—a pile of mismatched, chaotically implemented content with no direction—Fiend Folio is focused on bringing coherence to the game. Every floor (including variants) of the dungeon has been given a complete thematic makeover and a clear visual identity, aided by tons of excellently sprited decorations and literally dozens of beautifully animated and creative new enemies to complete each zone’s look.
Fiend Folio’s Necropolis is a clattering boneyard packed with skeletal creatures. Gehenna is a spa retreat for cenobites, full of chains, whips, blades, latex and leather. The Depths are truly haunted, full of ghosts, specters and other semi-corporeal critters. Special mention goes to the Sleeper; an invincible slow-moving monster that floods the screen with static and fog and pursues you until it either hurts you or you clear the room. It’s an exciting change of pace.
If there’s one downside to Fiend Folio, it’s that it makes an already chaotic game even less predictable. There are more chances to struggle with terrible items, or cruise through the game with a completely overpowered build. Many of the new enemies are a bit more demanding than the old guard, so it's perhaps not a mod for first-time players. Still, it’s an astounding piece of work in terms of quality, scale and aesthetic coherence.
The community seems to agree, as a growing number of mods are rolling out compatibility patches, allowing them to be run in parallel with Fiend Folio. For many, this is the new baseline Binding Of Isaac experience. The Fiend Folio team also recommend pairing their mod with the bouncy and playful Excelsior soundtrack mod (by RENREN) and melee-centric character Bertran (by melon & Deadinfinity) who has several special item synergies with Fiend Folio’s new equipment.
Fiend Folio isn’t the only major mod for the game, of course. For those wanting a (slightly) less grim and grisly take on Isaac, The Binding Of Undertale (abcbadboy, Cake & Wright) switches up Isaac’s ‘dead babies wallowing in feces and blood’ aesthetic for the cheerful world of Toby Fox’s friendly RPGs Undertale & Deltarune. Turns out that a colorful lick of paint and some cheerful new tunes go a long way.
So long as you don’t go in expecting a total conversion (most of the enemies are untouched, so there’s still some bodily fluids) there’s a lot to like here, including a large cast of new playable characters with new items and abilities. Deltarune is even represented up to its second chapter, with a whole second set of characters unlockable.
And lastly, if you want something completely different, how about a First Person Shooter mode? This mod by Nato Potato and Gummy lets you play the game from Isaac’s perspective through the magic of '90s Sega arcade-style sprite scaling tech. Obviously this is difficult, a bit clunky and far from optimal, but it’s proof that some truly wild stuff is possible with Isaac’s mod tools. Who knows what the future will bring?
General tips & tricks
Advice so good you’ll want to cry
⭐Turn it off then on again, especially when you’ve just downloaded several big mods. BoI: Repentance is known to be a bit unstable if you just try to leap into a major mod immediately after unpacking it. Before you play, quit and reload the game once to improve stability. The same applies after uninstalling mods, too. Load, quit, load again.
⭐Develop a sixth sense for secrets. Secret rooms (opened by bombing walls) follow clear enough rules that experienced players can often deduce their location. Secret rooms are almost always adjacent to 2-4 other rooms. Each of those rooms will have an unobstructed path (enemies aside) to the bombable wall. Super-secret rooms are dead ends attached to only one other room, making them harder to locate, but are usually found near the boss chamber.
⭐Knowledge is power, which is why you should pop open your in-game options menu and enable ‘Extra HUD’ and ‘Found HUD’. The former shows what permanent items you have, the latter shows your character stats and how items have modified them - especially handy as many items have unmentioned side effects. If you’re lucky enough to have an ultrawide monitor, the extra info gets placed in less intrusive locations too.
⭐Be Like Icarus, there’s no sun down here in the basement anyway! There’s a good number of items that give you permanent flight. Learn them and grab them wherever you can. It’s one of the most useful perks to have. No longer are spiked floors a threat, or the various harmful fluids that monsters can leave behind. It also lets you access a lot of areas and items blocked off by chasms, or just fly over rocky barriers. A few characters even start with this invaluable ability.
⭐Consider a controller. As well as offering full analogue movement for greater precision, having every feature under your fingertips at all times just feels good. Better still, you can switch between the right stick and face buttons for shooting, ideal for charge-fire weapons or modded characters that do actions on a double-tap. It’s my recommended way to play, but failing that…
⭐Mice are nice. Bizarrely, the game contains a hidden option to aim and shoot with the mouse, and enabling mouse use in some other mods like GoodTrip. In Windows, navigate to your [Documents\My Games\Binding of Isaac Repentance] directory and pop open the Options.ini file. Look for the line that says ‘MouseControl=0’ and change it to ‘MouseControl=1’. You may need to re-apply this tweak after changing in-game settings.
⭐Challenge Everything, just not like EA. Once you’ve finished that initial successful run and tenderized Isaac’s mom, there are a baffling number of options available to you. Beating the game with a given character will unlock more stuff. Completing special missions from the challenge menu will net you specific gear. Cranking up the difficulty to Hard will provide its own set of rewards (and suffering). Chase those achievements, as Isaac rewards almost all of them with tangible long-term perks.
⭐Play It Your Way. Because videogames are meant to be fun, and if you’re not enjoying anything about The Binding Of Isaac, there’s probably a mod to change it. Want to customize the spawn tables? You can do that. Just unlock everything? Sure, why not. Chasing goals and hunting for achievements can be satisfying, but sometimes you just want to curl up in a nice cozy basement and have a little cry. Don’t we all?
