A Monster Surge is an event that only occurs during the Mythos Phase.
This event will only occur during the "Open Gate and Spawn Monster" action of the Mythos Phase. A monster surge will be triggered when the Gate card indicates that a gate should open on a location in Arkham that already contains a gate token. If this is the case, the first player must randomly draw a number of monsters from the monster cup equal to the number of players or the number of open gates in Arkham, whichever is greater. These monsters are distributed evenly between the open gates in Arkham. Monsters placed in Arkham due to a Monster Surge follow the rules for monster limits in Arkham and the monster limits for the Outskirts.