Monster Manual is an unlockable activated item.
It is a book with a centaur, horse, and a dragon on its cover.
- Brother Bobby
- Level 2 or 3 Cube Of Meat
- Halo Of Flies
- Distant Admiration
- Sister Maggy
- Little Chubby
- Little Gish
- Little Steve
- Guardian Angel
- Demon Baby
- Forever Alone
- Combined with items such as the 9 Volt, Habit, etc. can allow Isaac to have an army of familiars following him. Using this in a boss room can cause the boss to lose health very rapidly.
- The item and its graphics are both references to the D&D Monster Manual.
- Its presence is related to the statement that D&D is a gateway to Satanism.
- The secret pop-up for this item misspells Monster Manual as "Monster Manuel".
- More than 3 orbitals may be active as a result using this item; this may have been done to avoid deleting old orbitals by accident, or could have been simply overlooked.
- Will spawn "undefined," if too many familiars are present on screen.