The terror level (as marked on the terror track) represents the current mental state of Arkham city's inhabitants. Certain game events, such as too many monsters entering the Outskirts or certain Mythos cards, can cause the terror level to increase - causing store locations to close and allies to leave town. If the terror level becomes too high, Arkham city becomes completely overrun with monsters.
At the beginning of the game the terror level on the Terror Track is set to 0. Each time the terror level rises the terror level marker is advanced along the terror track and one Ally card is removed from the Ally deck and returned to the box. Allies removed this way are no longer available for the rest of the game. If all Allies have been removed from the Ally deck this specific result has no effect.
If playing with the Dunwich Horror or Innsmouth Horror expansions, the terror level increases whenever a monster enters a vortex space.
- If the terror level reaches 3, the General Store is closed. Any investigators or monsters on this location are moved to the Rivertown street area.
- If the terror level reaches 6, the Curiositie Shoppe is closed. Any investigators or monsters on this location are moved to the Northside street area.
- If the terror level reaches 9, Ye Olde Magick Shoppe is closed. Any investigators or monsters on this location are moved to the Uptown street area.
If the terror level reaches 10, Arkham is overrun and the monster limit is removed for the rest of the game. Return all monsters in the Outskirts to the cup.
- Charlie Kane has a special ability to prevent the terror level from increasing by spending two clue tokens. His Personal Story can increase or decrease the number of tokens require.
- If Tommy Muldoon passes his personal story, the next time the terror level is increased, it is prevented.
- Discarding the Director's Diary Tome will reduce a terror level increase by 1, preventing an increase if it will only raise by 1.