The Fiend Folio

The Fiend Folio
Flavor text	"Summon fiendish friends"
Recharge Time	4 rooms
Item Pool	Library Treasure Room Treasure Room
Quality	2
Item Tags
Unlocked By	Get every Hard Mode completion mark as Fiend

The Fiend Folio is an active item added in The Reheated Update.

Effects

• On use, summons one of the following bosses/sets of enemies from the Fiend Folio MOD to fight for Isaac in the room for a short amount of time, each one doing various attacks:
  • Battie: Charges down from the top of the screen homing slightly towards enemies and wrapping vertically around the room several times, all while leaving a trail of blood projectiles that float in place for a short moment. After charging across the screen 3 to 5 times, Battie finishes it off with a slam from off-screen directly onto any remaining enemies, leaving behind rock shockwaves in a circle. After completing her slam attack, Battie will fly away.
    • Battie and her rock shockwave slam deals 10 damage per tick on contact, while projectiles she creates during her charge deal 3.5 damage.
  • Monsoon: Slams down directly onto an enemy from above, splashing water projectiles around him upon landing. Right afterwards, spits out a large Monstro-style cluster of projectiles towards any other enemies before ending their attack by splitting himself into a friendly charging Dribble.
    • Monsoon's initial slam attack deals 100 damage on a direct hit upon landing. Monsoon also deals 2 damage per tick on contact with enemies, while his projectiles deal 3.5 damage.
  • Technopin: Burrows out of the ground from a random location in the room before quickly aiming and firing a Technology laser towards an enemy that bounces once off of walls, similar to the Rubber Cement synergy. Technopin will perform this attack up to 3 times.
    • Technopin's laser deals 25 damage, and any enemies that happen to be in contact with Technopin themselves during this brief moment will also take 2 damage per tick.
  • Buster: Charges through the screen three times, while leaving a trail of fire. During the charge, several friendly Commissions are summoned. After the 3rd charge, Buster will stop in place and fire two lobbed projectiles that create rings of six flames. If there are any Commissions around, Buster will aim the projectiles at them. After that, Buster will leave the room.
  • Pollution: Charges across the middle of the room three times, leaving a trail of flames behind. When in the center, slows down for a brief moment to perform one of three attacks. Each attack will be done once and the order in which the attacks are done is always random. The attacks are as follows:
    • Spits out six friendly Blots.
    • Swipes with his bike, releasing an arc of 6 flames towards the nearest enemy.
    • Spins his bike, releasing three spinning lines of blood shots around him.
  • Slammers: A set of 8 Slammers and their variants, one after another, stomp down on enemies, dealing damage. The type of the summoned Slammers is determined as follows:
    • First two Slammers are always Wimpies.
    • 3rd and 4th Slammer are normal Slammers.
    • 5th, 6th and 7th Slammer can be a random Slammer from the list below:
      • S'More: When landing, creates a line of gunpowder in a random direction and ignites it upon landing.
      • Hoster: Upon landing, raises its skull to fire a spread of 3 blood shots at the nearest enemy.
      • Quaker: Upon landing, releases 4 rocks in cardinal directions and causes rocks to fall from the ceiling onto enemies for a short while.
      • Flinty: Just before leaping off-screen, creates an explosion (the explosion does not create a pit).
      • Smasher: Upon landing, creates a puddle of red creep and splatters a few blood shots around.
      • Stoney Slammer: Upon landing, creates a short-ranged rock wave.
      • Cracker: Upon landing, releases four rib projectiles that travel outwards before returning to the Cracker.
      • Slimer: Upon landing, creates a puddle of black, slowing creep and releases three tar projectiles that also create black creep.
      • Shaker: When landing, creates a line of salt in a random direction and causes salt projectiles to fall in that line upon landing.
      • Rancor: Upon landing, charges in a random direction until it hits a wall and then leaps off-screen.
      • Marzlammer: Upon landing, releases three wavy lines of white projectiles and spawns a friendly Small Maggot.
      • Doomer: Shortly after landing, fires Brimstone lasers in each cardinal direction.
      • Stompy: Upon landing, creates a small puddle of red creep and releases a short-ranged ring of 5 blood shots.
      • S'Eptic: When landing, creates a line of green creep in a random direction.
    • 8th Slammer is always a Thwammy.
• The Fiend Folio contributes towards the Bookworm transformation.

Notes

• Leaving the room while any spawned friendly bosses or enemies are still in the room will cause them to disappear. This doesn't include the friendly enemies spawned by Monsoon, Buster, Pollution or Marzlammer, however, who will persist between rooms.
• Using The Fiend Folio in a room with the Battie boss will cause the friendly version of Battie to always spawn. When the friendly version of Battie slams down, it will instantly kill the hostile Battie and spawn the Baby Badge.

Interactions

• Car Battery: Summons 2 random bosses/sets of enemies instead of one.

Trivia

• The Fiend Folio was an unused item in The Binding of Isaac: Afterbirth+ edition of the Fiend Folio MOD.
  • In the Afterbirth+ edition of the MOD, it was debated whether Fiend should start with this item once it's unlocked.
• The Fiend Folio makes a cameo appearance in the background of the updated loot card backdrop for card-type pickups in The Binding of Isaac: Four Souls - Requiem.
  • One such card to use this new backdrop is "Fiend Fire", which also includes a cameo appearance of Fiend in its artwork.
• The item, and by extension the name of the MOD itself, are a reference to Dungeons & Dragons; specifically, the name of three separate supplemental volumes for D&D known as Fiend Folio — a compendium of monsters for use in the tabletop game.
  • The title of the MOD is consequently a pun, as not only is the usage of the reference to the D&D book due to the MOD being explicitly advertised as adding hundreds of new enemies for The Binding of Isaac, it is also named after the titular character of the MOD itself. However, this wordplay in the name is inadvertently due to coincidence, as Fiend himself came very late in Fiend Folio's development in Afterbirth+, after the name was already conceptualized.
• Buster and Pollution appearing as one of the effects from using The Fiend Folio were unused prior to The Spitshine Update. The same update had also added Slammers to the list of effects.

Gallery

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  The "Big Book" splash image seen when The Fiend Folio is used.