When an investigator is stunned, the token is placed on his Character card. When a monster is stunned, the token is placed next to its figure.
These tokens affect monsters and investigators differently as follows.
Investigators: A stunned investigator only receives one Movement Step during his turn. If he becomes stunned during his turn, he may not take a second Movement Step. In addition, he receives –2 to every attribute test. The effects of stun tokens do not stack (that is to say, having two stun tokens does not give the investigator –4 to each attribute test).
Note that this penalty only applies to attribute tests (i.e.,rolling the die and comparing it to an attribute) and does not lower the attribute for other purposes. For example, this penalty does not reduce the number of puzzle actions an investigator receives.
Monsters: A stunned monster may not move or attack. An investigator or monster may have multiple stun tokens on him, and may only discard one per turn (either during the Investigator Trading Step or the Monster Attack Step).