What's the difference between an Invader and an Explorer (the stick figure)? Explorer refers only to that type of piece, represented both on cards and on the board by a figure of a person. Invader is a generic term, referring to any of the types of pieces representing the settlers, i.e., an Explorer (stick figure), Town (two buildings), or City (three buildings).
If a rule tells you to do something to an 'Invader', like on Level 3 of the Fear card Isolation, it refers to any one of the three types. If it tells you to count Invaders (like on that same Fear card), it is counting any of the three types equally.
Some Fear Cards remove Invaders based on Health rather than quantity. Those consider all modifiers to current Health (from, e.g., England Level 5, or an Event/Fear card) - but not Damage, as Damage does not reduce Health. (Health is simply how much Damage it takes to destroy something.) (Discussion elsewhere) Tags: Invaders, Remove, Health, Isolation (Fear card), 1 more...
