Monster markers represent the monsters roaming the streets of Arkham. Each monster has two sides: a movement side and a combat side. Leave the monster’s movement side face up while it wanders around the board. When an investigator battles a monster, flip the monster marker to its combat side. Players may look at either side of any monster marker at any time.
Most monsters move during the Mythos phase, after any gates have been opened and clue tokens have been placed. The player who drew the mythos card looks at the bottom-right corner of the card to determine monster movement. The black and white boxes on the card contain dimensional symbols; each monster that has a matching dimensional symbol moves along the black or white track for its current area. Exceptions: Monsters that are in the same area as an investigator do not move and remain in place. No encounter takes place with the monster during this phase, but the investigator(s) will be forced to fight or evade during the next Movement Phase. Also, some monsters have special movement rules depending on their color (see below).
See main article at Monster movement
- Normal (Black Border): Normal monsters move as described above.
- Stationary (Yellow Border): Stationary monsters do not move. Outside of abnormal encounter or item effects, they remain at the location where they entered play.
- Fast (Red Border): Fast monsters move twice, following the appropriate arrows for both steps of their movement. Fast monsters stop moving immediately, however, if they encounter an investigator.
- Unique (Green Border): Monsters with unique movement (such as the Hound of Tindalos) have special movement abilities listed on the combat side of their marker. Turn such monsters over and follow their instructions for movement.
- Flying (Blue Border): Flying monsters generally move directly towards the nearest investigator in a street area, or move to the Sky holding area if they can't reach any investigators this turn. Flying monsters already in the Sky when they move may swoop down on an investigator in a street or at Devil Reef.
- Stalker (Purple Border): Stalker monsters move like normal (black border) monsters unless an investigator is in an adjacent street area or unstable location, in which case they move to that area.
- Aquatic (Orange Border): Aquatic monsters move like normal (black border) monsters unless they are in an aquatic location (the River Docks or Unvisited Isle in Arkham, or one of several places in Kingsport and Innsmouth) and there is an investigator in a different aquatic location. In that case, the monster instead moves to that investigator's space.
See main article at Combat.