Add several new never-randomly-generated cards, all of which are designed to give strong but short buffs, to you and more often allies. Though their frequencies are 0, they are sometimes dropped from monsters you and your pets kill, at the same frequency the keyed create monster cards do.

Other roles can write these scrolls if they want to or find them in bones, but they are generally intended to be less powerful than many existing scrolls so they shouldn’t steal generation probability from them.