A Devastation Encounter is a type of Encounter found in Eldritch Horror. They are only used when Shudde M'ell is the Ancient One, or by using some type of Prelude that would allow for a Disaster to be put in play.
If an Investigator is on a space marked with a Devastation token, they have the option of resolving a Devastation Encounter. Like an Expedition Encounter or Mystic Ruins Encounter, they typically are resolved in multiple parts. However, often times, the player has the choice of which of the two effects to resolve.