Monster Manual

Monster Manual is an activated item.

Effects

When used, a random familiar will be spawned from the following:

Familiars spawned by Monster Manual last for the current room.
Familiars spawned by Monster Manual last for the rest of the floor.
Familiars generated by Monster Manual do not contribute toward transformations.
This item belongs to the Bookworm set. Collecting three items from this set will transform Isaac into Bookworm.

It can spawn familiars not yet unlocked.
If Cube of Meat or Ball of Bandages are spawned and Isaac already has either of those items, the level of these items will increase while the effect is active.
Using Monster Manual is a good method to unlock achievements related to Super Meat Boy and Super Bandage Girl.
- Using Monster Manual and enough Lil' Batteries, Super Meat Boy and Super Bandage Girl can both be achieved in the same run.
- If Isaac does not already have the Cube of Meat or Ball of Bandages, Monster Manual can spawn a level 2 Cube of Meat or Ball of Bandages in one use.
Mongo Baby will not copy familiars spawned by Monster Manual.
Familiars spawned by Monster Manual cannot be rerolled into other items by D4 or D100.
Box of Friends will not duplicate familiars spawned by Monster Manual.
Tinytoma orbitals will persist between floors until they are all destroyed. They will not respawn outside of the floor they were generated in.
The familiars summoned by Monster Manual are items with a monstermanual item tag.
Tainted Lazarus: If dead Tainted Lazarus has used Monster Manual, but living Tainted Lazarus progresses to the next floor (or vice versa), familiars from the previous floor are not removed. Upon exiting the game, or moving to the next floor as either character, any familiars retained this way are lost, meaning familiars cant be kept at most 1 extra floor.

Book of Virtues: Spawns wisps in the inner ring. The given wisps function similarly to familiars given by Buddy in a Box.

Sacrificial Altar: Summoned familiars can be sacrificed since they persist for the entire floor, even if Monster Manual isn't currently being held.

In the original The Binding of Isaac, due to a typing error this item was called "Monster Manuel". This has been corrected for Rebirth.
- Monster Manual may sometimes display the misspelled name when picked up.
Monster Manual is a direct reference to Dungeons & Dragons. Its appearance in the game closely resembles the Advanced Dungeons & Dragons First Edition Monster Manual.
- The item being in the Devil Room pool is likely a reference to the moral panic surrounding the game in the 1980s.