Book of Virtues: 50% to spawn an eternal white glowing wisp, on the middle ring, which cannot be destroyed. Every use has a 50% chance to destroy all the wisps instead of spawning another. Does not affect wisps other than the ones made by this item. Rerolling items does not affect this chance.
This item functions similarly to the D6 in the Eternal Edition of the original Binding of Isaac, where it had a chance to delete the item instead of rerolling it when playing on hard mode.
This item's collectible sprite refers to it as "Florian's D6".
The secret popup for this item even depicts Florian Himsl lovingly rubbing said D6, indicating he really likes this item. Florian having a chance to drop Eternal D6 in the Ultra Pride fight is also a nod to that.