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.
|Achievements||Attributes||Bosses||Cards and Runes||Challenges||Chapters|