Npc tokens do not have a way to choose passive perception from the dropdown list of choices. It'd be really nice to be able to add passive perception to the token bars and have it quickly visible as this stat is used often enough. In the sheet passive perception goes in the "senses" text field which can have more than just the passive perception listed, so it doesn't work to use. There is a passive_wisdom listed in the dropdown but it only calculates correctly for player characters. This subject has been discussed recently and often in the past. Proposal: Have the passive_wisdom field correctly calculate passive perception for both players and npcs, or add a new "npc_passive_perception" to the dropdown list of attributes you can assign to a token bar.
