A book bound in leather made from human flesh, with an impression of a screaming face on the cover.
Upon activation, all enemies in the room will be damaged.
- Bloody Lust/Samson's Lock - All enemy projectiles in the current room are also destroyed upon use, which will count as "kills" for the extra damage effect.
- Triggering the effect of the trinket A Missing Page will also count towards unlocking The Necronomicon.
- This deals significant damage during the mom fight as it hits all the doors and the leg, leaving mom with little health left.
- The Necronomicon is a fictional grimoire appearing in the stories of horror writer H. P. Lovecraft.
- It is believed to be bound by human skin, explaining the face on the cover.
- The book bears a strong resemblance to The Necronomicon in the Evil Dead series.
- Using the Necronomicon on a Mask + Heart will only kill the 'masks', leaving the hearts alive, but one hit away from death. This is not due to the item itself so much as the damage value exactly bringing a Heart to 0HP.
- In the Collection, the Necronomicon is spelled "Necronomico".
- The Necronomicon can hit off-screen enemies like with The Candle.