Often when I'm running a game, I focus on antagonist NPCs, characters who force me to think about what they're doing and how the player characters can react to their activities. It is rare when an allied NPC gets spotlight time, which brings me to this idea of "checklist NPCs". The NPC is associated with a checklist of prompts or events that best represent their purpose in the game. A player can check an item off the list to bring that event into play.