Binding of Isaac: Rebirth Wiki
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Binding of Isaac: Rebirth Wiki
Backasswards
Character Isaac appearance.png
Full red heartFull red heartFull red heart
Table dividing line 1.png
Challenge Number
31
Starting Items
8-10 random items
Available Rooms
Item Pool Treasure Room.png: no          Item Pool Shop.png: yes
Unlock Method

Backasswards Removed in Repentance Defeat ??? or The Lamb
Added in Repentance Defeat Mega Satan

Added in Afterbirth †

Backasswards is challenge #31. Isaac starts on the Mega Satan boss fight with 8-10 random items and 10 Heart Containers (exact number may vary based on the items). The goal is to play the floors backwards, hence the challenge's namesake. Every floor ascended will cost one Heart Container (if the player has no Red Hearts, it will take a Soul Heart instead), and the oldest item in the inventory. The player starts each floor with a boss fight (except the Dark Room Dark Room, which can be immediately completed), and will have to find the "starting room" to ascend a beam of light to the "previous" floor, similar to the effect of Added in Repentance15►Dad's Note Dad's Note.

Difficulty[]

Starting with a random selection of items, and starting on the Mega Satan boss fight makes this challenge very difficult at first. If Mega Satan and Satan can be defeated, the rest of the challenge becomes significantly easier. However, no bosses need to be defeated to progress - teleporting out of boss rooms can make the challenge much easier. While treasure rooms are disabled in this challenge, bosses will still offer a reward upon defeating them.

Strategy[]

  • Try to get some really powerful few-item synergies. Resetting is a perfectly good way to ensure good items.
    • Since Isaac will have at least 10 Red Heart containers from the start, 15►Pyromaniac Pyromaniac and items that grant exploding shots (15►Ipecac Ipecac, 15►Dr. Fetus Dr. Fetus, and 15►Epic Fetus Epic Fetus) combined is game breaking since as long as he gets caught by his explosions, he can heal indefinitely. They also do plentiful damage to enemies and can open closed doors. Isaac also can heal from Mega Satan's rock waves and mini-bosses spawned by him which spawn ignited Bombs, Troll Bombs or Megatroll Bombs.
    • Having 15►Gnawed Leaf Gnawed Leaf and something that can do damage while not moving, such as 15►Daddy Longlegs Daddy Longlegs, 15►Dead Bird Dead Bird, or 15►Smart Fly Smart Fly, can basically guarantee an eventual win. Damaging orbitals are also a big help. Finally, size-decreasing items, such as Added in Repentance15►Pluto Pluto or items that block bullets, such as 15►Trinity Shield Trinity Shield will drastically reduce the difficulty of most of Mega Satan's attacks.
    • 15►The Wafer The Wafer is an extremely useful item to receive in this challenge as well.
  • Even without powerful items or synergies, the challenge of Mega Satan (or any other boss) can be skipped by teleporting out of the room.
    • Isaac only needs a starting item that produces a tarot card on pickup, such as 15►Magic 8 Ball Magic 8 Ball or 15►Starter Deck Starter Deck. Added in Repentance15►Booster Pack Booster Pack has a high chance to produce a card that can teleport Isaac since it spawns 5 random cards. 0 - The Fool 0 - The Fool, IX - The Hermit IX - The Hermit, and XVIII - The Moon XVIII - The Moon are all viable teleportation cards.
    • 15►Cursed Eye Cursed Eye also works as a method of teleportation, but can come with the downside of unwanted teleportation.
    • Teleportation through resurrection by means of items like the 15►Ankh Ankh is possible but dangerous since most resurrection items revive Isaac with very low health.
  • Taking a hit from Mom's Hand brings Isaac to the starting room of a floor.
  • Going up a floor will remove one heart container and one passive item. If Isaac only has one red heart container, something as simple as leaving the floor itself will end the run.
    • For this reason, be wary of taking devil deals at low health.
    • 15►Dead Cat Dead Cat in particular can be a run-ender, as it removes all but one red heart container on pickup. Additionally, starting with this item will make the Mega Satan fight extremely hard due to the large health reduction it causes.
    • Beware of 15►Experimental Treatment Experimental Treatment too, as it has a chance to remove heart containers.
    • Soul Hearts and Black Hearts are not affected by this if Isaac has any red heart containers. Thus, 15►Guppy's Paw Guppy's Paw is an extremely useful item for this run.
  • Shops spawn as normal above Womb Womb.
  • Rune of Ehwaz Rune of Ehwaz and 15►We Need to Go Deeper! We Need to Go Deeper! generate closed exits to the next floor, so they cannot help Isaac skip the current floor.
  • Items to be removed first are the "first" items picked up. This is the item in the rightmost column, in the lowest row of that column. If powerful items are shown there, it is best to restart.
  • Removed in Repentance If a Mom's Dressing Table spawns in the starting room, its icon will show up on the map even if the starting room has not been visited yet. This makes finding the passage to the previous floor significantly easier.

Reward[]

Notes[]

  • Teleporting to the Dark Room through Sacrifice Room brings Isaac back to Mega Satan's fight, and all previously encountered floors will be regenerated.
  • 15►Halo of Flies Halo of Flies will take two entire floors to be removed. Only one fly will be lost per floor.
  • Added in Repentance15►R Key R Key will teleport Isaac back to the Mega Satan fight.
  • Using Genesis after Dark Room may softlock a run, because the exit generated in the bedroom is closed. Escaping the room is possible if any item or pickup that allows escaping is generated. (eg. 15►Teleport! Teleport!, 15►Forget Me Now Forget Me Now)
  • The Lamb cannot be encountered in the Dark Room.
  • Only 15►The Negative The Negative can be picked up after defeating It Lives.

Bugs[]

Bug Bug! While entering an exit to the previous floor, if the player kills the process (isaac-ng.exe) during the versus screen before a boss fight, re-entering the game will lead Isaac to the starting room of the previous floor instead of the boss room. This allows the player to finish the challenge pretty easily without any actual fights.
Bug Bug! Sometimes the layout of the rooms makes traversing to the previous floor impossible. There might be a hole where the light is supposed to be and without flying, makes the run impossible to beat.
Bug Bug! If Isaac is teleported into the I AM ERROR room on the final floor of the challenge, there will be no exit, making the run impossible to beat.
Bug Bug! After the Mega Satan fight the player may start the following floors already in the beam of light making the Mega Satan fight the only one in the challenge. If the player doesn't have enough health to make it to The Basement 1, the run is over. If the player has enough health to make it to The Basement 1 they will be unable to move, to rectify this, simply exit the run, re-enter it and claim the reward.
Bug Bug! Star of Bethlehem will cause the game to instantly crash. The only solution is to restart the challenge, as the Continue option will keep crashing.


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