Backasswards is Challenge #31. Isaac starts off with 8-10 random items, and start on the Mega Satan boss fight. The goal is to play the floors backwards, hence the challenge's namesake. Every floor ascended will cost the oldest item possessed and one red heart container. The player starts each floor with a boss fight (except the 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.
Starting with 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.
- 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, PyromaniacIsaac heals 1 heart instead of taking damage from an explosive source. Adds 5 bombs. and items that grant exploding shots ( IpecacReplaces tears with explosive and poisoning projectiles fired in an arc from the mouth., Dr. FetusTears are replaced by bombs that benefit from bomb-enhancing effects and slide for a fixed time after being fired., and Epic FetusIsaac's tears are replaced with guided missiles, like those used by the Doctor's Remote.) combined is gamebreaking since as long as he gets caught by his own 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 bombs, troll bombs or mega troll bombs.
- Having Gnawed LeafAfter standing still and not shooting for a short time, Isaac turns invincible until he moves or shoots. and something that can do damage while not moving, such as , Dead BirdSpawns a flying familiar for the current room that chases enemies whenever Isaac takes damage., or Smart FlyAfter Isaac takes damage, this fly will deal continuous touch damage to whatever enemy caused the damage until it is dead. The fly will then systematically attack 1 enemy at a time until the room is cleared., can basically guarantee an eventual win. Damaging orbitals are also a big help.
- The WaferAll sources of damage that would cause more than one half heart of damage are reduced to one half heart instead. is an extremely useful item to receive in this challenge as well.
- 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.
- With resurrection or teleportation items (such as Teleport or Cursed Eye), it's possible to skip boss rooms by dying as being resurrected puts Isaac outside of the room rather than back on the previous floor.
- Despite this, do not get the Dead CatSets the amount of red heart containers to 1, but gives Isaac 9 extra lives. After dying, Isaac is teleported to the last safe room. New heart containers can be obtained after picking up this item, but after each death, the number of heart containers is set to 1 again.. If attempting to move onto the next floor while only having 1 HP, Isaac will instantly die instead of progressing, wasting one of his lives in the process.
- Likewise, do not get Ankh. If resurrected as ???, each time ascended a floor a soul or black heart will be lost, increasing the difficulty of the challenge.
- Shops spawn as normal above The Womb.
- 0 - The Fool tarot card and Mom's Hand are both quick ways to get to the starting room.
- Ehwaz and We Need to Go Deeper!Creates a trapdoor to go to the next floor. If used in The Womb, it will create a trapdoor to Sheol, even if the player hasn't unlocked it. 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.
- Halo of FliesSpawns two pretty fly familiars that block enemy shots and deal contact damage to enemies. will take two entire floors to be removed. Only one fly will be lost per floor.
- If a 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.
While entering an exit to the previous floor, if 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 previous floor instead of the boss room. This allows the player to finish the challenge pretty easily without any actual fights.
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.
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.
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 Basement 1 they will be unable to move, to rectify this, simply exit the run, re-enter it and claim the reward.