Terrifying spellbook Donut has read but is scared to use, whose effect Mordecai told her to keep secret.
Talking about the scared war mage guys, Donut admits she ended up reading one of the spellbooks — the one that bleeds and cries — but says she is kind of scared to use it, and worried that even so it won't be enough. Mordecai told her not to tell people what it does.
Carl answers that they can only fight one battle at a time, and that luckily they aren't doing it alone. Privately he notes he still hasn't opened the box that gave her the spell, and that the Gate of the Feral Gods remains in his inventory as another weapon of mass chaos waiting to be unleashed.
A spellbook that bleeds and cries, disturbing enough that its own reader hesitates to use what it taught her.
Donut's secret reserve weapon, deliberately undescribed on Mordecai's advice.