Carl and Donut's set of named, pre-agreed combat plays for coordinated reactions in a fight.
The playbook is the system of named combat 'plays' Carl devises with Princess Donut after the Mold-Lion fight taught him the value of canned, coordinated reactions. Each play has a name; when either partner calls it, both instantly follow a predetermined set of actions without question, so they always know what the other is doing. Their first play, 'Panic,' is simple — Carl casts Fear, Donut follows with a Magic Missile — with plans to build more complex plays that integrate Mongo as they train.
The party's growing tactical language for coordinated combat.