Aprils Fool is challenge 32. Isaac has no special starting items for this challenge. However, all floor bosses are changed to The Bloat, Stonies have a chance to be replaced by Cross Stonies, all items, trinkets, and pickups display an incorrect sprite, activated items and pickups never activate the correct effect, and Isaac's location is displayed as a random room on the map. The goal is to defeat Mom's Heart, which has also been replaced by The Bloat. Treasure Rooms and Shops are present in this challenge.
All changes mentioned above are designed to make this challenge exceedingly difficult and frustrating.
While Curse of the Blind is not active, the fact that all pedestal items are displayed incorrectly means that, like with Curse of the Blind, it is impossible to know what each item is until acquired.
All items are still pulled from the correct item pool (Angels will still drop Key Pieces, Mom will drop The Polaroid and The Negative if they are unlocked).
Pickups (coins/hearts/bombs/keys), unlike pedestal items, are not displayed incorrectly. Once a pickup is acquired, it is randomly changed to another.
Coins and keys give hearts, bombs or keys.
Bombs give hearts, coins or keys.
Hearts give coins, bombs or keys.
This makes it very hard to accumulate coins as they can be gained only from bombs and hearts, at a 1 in 3 rate.
Lucky Coins will still provide +1 Luck.
Hearts follow their standard behavior, and cannot be picked up unless Isaac is injured, even though they provide other resources. However, other pickups may provide red hearts when picked up, giving no benefit if health is full.
All activated collectibles, pills, cards and runes have a random effect upon being used. This makes any strategy involving them unreliable and potentially dangerous. Cards can trigger the Suicide King effect, pills can activate the Health Down effect, and active items can trigger Plan C.
Cross Stonies are significantly more challenging compared to regular Stonies.
Most importantly, every single boss found during the challenge is The Bloat, which is normally found as early as chapter 3. As a result, the boss fights before chapter 3 will be more challenging than usual.
Randomness is a major source of difficulty in this challenge, but it can also be the key factor to completing it, as sometimes coins will grant Soul Hearts, Black Hearts, and Gold Hearts. If a large number of coins are found in one place, it is possible to dramatically increase Isaac's health pool. Gold hearts, in particular, are useful, as they can spawn a large number of coins when depleted, which in turn can be used to grant a large number of other pickups, potentially even more gold hearts. If lucky, enough gold hearts chained could lead to 99 of each pickup.
When Dimes or Nickels are picked up, they will grant 10 or 5 of the pickup they act as respectively, which can lead to incredibly powerful results, such as acquiring 5 Gold Hearts at once.
It is possible to use a Swallowed Penny along with a Sacrifice Room to generate infinite coins, assuming Gold Hearts are repeatedly spawned in the process. This also will trigger many of the Sacrifice Room's effects, notably transporting Isaac to the Dark Room. The challenge can still be completed by defeating The Bloat at the end of the Dark Room stage. This can be done as early as the first floor, allowing most of The Bloat fights to be skipped entirely.
Active items with a short charge time, such as Butter Bean, or no charge time, such as Kamikaze!, can allow for rapid use of random active item effects. While this can be extremely powerful if lucky, this can also trigger effects like Plan C, likely killing Isaac.
The map always displays Isaac's location incorrectly, randomly selecting a room on the floor for this purpose. As this includes rooms not yet uncovered through traditional methods, it is possible to learn Secret Room locations from this.
Although your location in the map isn't correct, the rooms you enter and cleared appear, revealing where you are if you check the map frequently: this becomes unreliable as you progress since, with larger maps, the indicated current location may be far enough away that your actual location won't be visible in the mini-map, though it always is visible with the full map displayed. This makes XL floors more disorienting.
Counterfeit Penny has a chance to grant coins upon picking them up, making it easier to accumulate coins.
Pills will always show their true effect in their name after being used, and the narrator will always state what the effect is, meaning that setting the narrator to always activate can be helpful.
As the Bloat has less health than other bosses chapter 4 onward including Mom and Mom's Heart, the player is less reliant on powerful items and Devil/Angel rooms, although they are welcomed.
Items that allow you to deal damage without directly aligning yourself with enemies such as Marked and The Ludovico Technique make the Bloat fight markedly easier, lowering the difficulty of the challenge significantly.
Not entering the Devil Room and waiting for an Angel Room to appear is less risky : because of the wrong display, the player will not know what item he will get with a deal.
Active Items that can be spammed like Magic Fingers and IV Bag (which is a fairly reliable find) open a lot of routes for this challenge. Bringing these items to either a Devil Room or Angel Room will allow the player to spam random item effects, and possibly generate many powerful items from those pools.
This challenge's effect of changing item appearance is similar to the April Fool's 2016 daily challenge.
The Bloat's appearance as a replacement for all other bosses is a reference to the exceptional hatred some fans express toward this boss.
The user who suggested this challenge was banned from a subreddit (NSFW) whose theme is hatred towards The Bloat. This same user was also forced to use the "I love The Bloat" flair for a week on the Binding of Isaac subreddit.