Seeds, essentially random strings of characters, are used as the basis for all decision making in the game. By inputting a seed manually, you can guarantee that most randomly-generated decisions will occur the same every time. For instance, two players using the same seed will find the same items in the same locations.
- With the exception of some special seeds, inputting a seed will cause the 'no trophies' mark to appear. This prevents any achievements from being obtained on that particular run.
- Special seeds do not affect level generation.
- All alphanumeric characters are accepted except for 5, I, O, and U. On the PC version pressing the I, O, and U keys during seed entry will replace them with 1, 0, and V respectively.
- Once a special seed has been entered, it will be permanently unlocked without needing to enter the code again. Pressing Q / Left Bumper during character selection will bring up the Easter Egg Section, in which any previously unlocked game mode can be selected. Selecting multiple modes at once is also possible.
|Infinite basements||The Basement repeats infinitely.|
|Tricky pickups||Pickups mimic Isaac's movements.|
|Pickups time out||Pickups quickly fade.|
|F2P version||Isaac starts with 69 coins, but all items and consumables must be bought.|
|Pacifism||Enemies do not take damage. All doors stay open. When in a boss room, the boss's health slowly drains.|
|Enemies respawn||Enemies, including bosses, respawn once Isaac leaves the room. Completing a room multiple times does not yield additional pickups.|
|Point of no return||Boss rooms lock Isaac in similar to the Mom fight.|
|Poopy trail||Isaac leaves a trail of poop behind him as he walks.|
|Dog mode||Isaac is invincible.|
|Kids' co-op mode||Makes co-op babies invincible.|
|Permanent darkness||Permanent Curse of Darkness.|
|Inescapable labyrinth||Permanent Curse of the Labyrinth.|
|Hopelessly lost||Permanent Curse of the Lost.|
|Forever unknown||Permanent Curse of the Unknown.|
|Unending maze||Permanent Curse of the Maze.|
|Incurable blindness||Permanent Curse of the Blind.|
|Horrible curse||Permanent Curse of the Cursed.|
|Illuminate darkness||Provides immunity to Curse of Darkness.|
|Escape the labyrinth||Provides immunity to Curse of the Labyrinth.|
|I once was lost||Provides immunity to Curse of the Lost.|
|Know the unknown||Provides immunity to Curse of the Unknown.|
|Stay out of the maze||Provides immunity to Curse of the Maze.|
|Heal the blind||Provides immunity to Curse of the Blind.|
|Total curse immunity||Provides immunity to all curses.|
|Full heart damage||Isaac takes a full heart of damage from all sources.|
|Twelve heart damage||Isaac takes twelve hearts of damage from all sources.|
|Don't stop moving||Isaac takes damage if he stops moving.|
|Damage on a timer||Every 45 seconds, a ticking will begin, and after 5 seconds, Isaac will take 1/2 heart of damage. Damage increases to 1 heart in the womb and below. Having invincibility during the time when damage should be inflicted prevents the damage.|
|30 minute limit||Gives a time limit of 30 minutes to beat the game. When the timer hits 29:45, a timer starts ticking, and after 30:00, Isaac takes damage every second.|
|Ice physics||Makes the ground slippery.|
|Bravery||Isaac fires tears in the same direction that he moves. Removes the normal ability to fire tears.|
|Cowardice||Isaac fires tears in the opposite direction that he moves. Removes the normal ability to fire tears.|
|Reversed controls||All movement and firing keys are reversed.|
|Axis aligned controls||Isaac cannot move diagonally.|
|Camouflage player||Isaac blends into the ground.|
|Camouflage enemies||All enemies blend into the ground.|
|Camouflage stuff||Pickups and items blend into the ground.|
|Camouflage everything!||Isaac, enemies, pickups, and items all blend into the ground.|
|Invisible player||Isaac becomes completely invisible.|
|Invisible enemies||All enemies become completely invisible.|
|The blank||Isaac has no face.|
|Grayscale||Isaac turns gray.|
|Christmas||Isaac wears a Christmas hat.|
|Big head mode||Isaac's head is large.|
|Tiny head mode||Isaac's head is small.|
|Black body||Isaac and his tears turn completely black.|
|Glowing tears||Isaac's tears glow.|
|Extra gore||Makes a lot more blood appear after enemies die.|
|Cathode rays!||Applies a filter that makes the game look like it's being played through a cathode ray tube.|
|Dyslexia||All in-game text is rearranged.|
|No HUD||Removes the HUD entirely. This affects the map, health, consumables, held items, pickup text, floor names, and more.|
|Mystery pills||All pill names and descriptions show ???.|
|Mystery cards||All card names and descriptions show ???.|
|Champion enemies||All enemies turn into champions if possible.|
|Charmed enemies||All enemies are permanently charmed.|
|Confused enemies||All enemies are permanently confused.|
|Scaredy enemies||All enemies are permanently scared.|
|Skittish enemies||Every few seconds, all enemies become scared.|
|Asocial enemies||All enemies are permanently charmed and scared.|
|Farty sounds||All sound effects are replaced with farts.|
|Movement tempo||Music speed is affected by Isaac's walking speed.|
|Health tempo||The lower Isaac's health is, the slower the music is.|
|Downtempo||Music is slowed down.|
|Downtempo--||Music is significantly slowed down.|
|Uptempo||Music is sped up.|
|Uptempo++||Music is significantly sped up.|
- While the BRTL B0NS seed is enabled, getting hit will not result in a death if Isaac possesses Red hearts as well as Soul hearts or Black hearts. Instead, the Soul hearts and/or Black hearts will be completely depleted, leaving Isaac with only his Red hearts.
- If the ICES KATE seed is enabled, purple champion monsters will be much more dangerous, as escaping their gravitational pull is almost impossible.
- Many of the special seeds can be found by using either the Fortune Teller or the Rules Card.
- Some special seeds were shared with the community by the developers.
- If an item that would appear on a seed isn't unlocked yet, it will be replaced by another item that is unlocked.
- The "DYSL EXIA" seed is a reference to dyslexia, a disorder that cause difficulties in spelling, reading, and writing.
- The seeds "ANDA NTE", "LARG HET0", "ALLE GR0", and "PRES T0" refer to andante, larghetto, allegro, and presto, respectively. These are names of musical tempos, which are the speeds of given pieces of music.
|Achievements||Attributes||Bosses||Cards and Runes||Challenges||Chapters|