Whenever it seems appropriate within the bounds of the narrative, you can give a PC advantage or disadvantage on a roll. This tool explicitly shows a player that the situation is helpful or harmful to the action they’re attempting. For example, if a player is attempting to sprint through deep mud or knee-high water, you might impose disadvantage on their Agility Roll. If they say something clever to a guard or use knowledge they obtained from an NPC about their captor, you might grant advantage on their Presence Roll.

NPC Advantage and Disadvantage

If an NPC has advantage, roll an extra d20 and take the highest result. Similarly, if an NPC has disadvantage, roll an extra d20 and use the lowest result. Some PC abilities can impose disadvantage on an NPC’s roll, or you might choose to give an NPC advantage or disadvantage due to the circumstances of the narrative.

Advantage vs. Difficulty

Because you control both Difficulty and advantage or disadvantage, why not just raise or lower the Difficulty of a roll instead? You certainly can, but advantage and disadvantage allow the characters’ actions and circumstances to modify how successful they are at interacting with the world in a tangible way. Players feel the advantage through rolling extra dice, while a disadvantage conveys a difficult situation on both a mechanical and narrative level.