Forbidden Folios

Location: The Occult Crescent: North Horn (X:34.7, Y:34.5)
Duration: 20 min
Knowledge: 400-260,420
Phantom EXP: 720
Tomestones: 20 10
Boss: Arbatel
Spawn Mob: Automatic
Patch: 7.55
Links: GT TC

With a giant sealed grimoire for a head, this well-read familiar lurks among dusty shelves and timeworn tomes. Unfortunately for the creature, the arcane techniques inscribed upon its pages pose too great a danger to ignore.

— In-game description

Forbidden Folios is a Critical Engagement spawned in The Occult Crescent: North Horn.

Rewards

Guide

Knowledge Level Correction: Deals moderate raidwide damage and inflicts all players with a Correction debuff ranging from +1 to +5. The debuff increases players' effective Knowledge Level.
Summon: Arbatel summons books that open up into various invulnerable adds that will cast spells that only affect players of a certain Knowledge Level. The first time Arbatel uses this ability, it will summon two adds that each affect half of the arena, while all future casts create three adds that affect one-third of the arena each.
- Page 8 (Moogle) will cast Knowledge Level 4 Holy, dealing lethal damage to players whose Knowledge Level is a multiple of four (20, 24, 28, 32, 36, 40, 44).
- Page 16 (Gargoyle) will cast Knowledge Level 3 Flare, dealing lethal damage to players whose Knowledge Level is a multiple of three (21, 24, 27, 30, 33, 36, 39, 42, 45).
- Page 64 (demon head) will cast Knowledge Level 5 Death, instantly killing players whose Knowledge Level is a multiple of five (20, 25, 30, 35, 40, 45).
- Page 512 (Dvergr) will cast Prime Knowledge Level Death, instantly killing players whose Knowledge Level is a prime number (23, 29, 31, 37, 41, 43).
  - Due to the nature of these attacks, the first Summon will always contain Page 512, to avoid situations where players may have a Knowledge Level that is a multiple of two numbers and thus make the attacks unavoidable. Likewise, it is also possible for the player's Knowledge Level to meet none of the summons' criteria, rendering the player completely immune.
Marginalia: Moderate raidwide damage.
Cover to Cover: A two-part attack that strikes one half of the arena, then the other half, dealing high damage.
Unbound Ink: A circle AoE centered on Arbatel. Immediately follows Cover to Cover.
Book Drop: Several three-person tower AoEs will appear randomly around the arena. The amount of towers scales with the amount of players participating in the Critical Engagement. While this is happening, overlapping checkerboard AoEs will criss-cross across the arena.
Fire II: Four cone AoEs fanning out from Arbatel's position. A second set of Book Drop towers will spawn during this attack.
Arcane Rule: Two perpendicular line AoEs cross in the center of the arena, then gradually cascade outward.
Blot: A line of three large circle AoEs cover the center of the arena, then more lines of circle AoEs appear to the sides. Players should stand in the circles that spawned last, then move into the center once those AoEs resolve.