Yes and no. Here's Ashrian's Heroic Feat:
Ashrian's Heroic Feat wrote:
[Action]: Choose a monster within 3 spaces of you. Each monster in that monster group is Stunned.So when I say "yes and no," what I mean by the "no" part is that you cannot choose a monster for the first part who is behind a closed door.
Descent 2nd Edition rulebook, page 13, Counting Spaces wrote:
Some abilities require players to count the spaces from a figure to the target of the ability. When counting spaces for attacks and abilities, players ignore any non-obstacle terrain in those spaces (see “Terrain” on page 18). The player just needs to verify that his target is in range for the ability to reach the target. If an ability affects figures within a specified number of spaces, line of sight is not needed unless specifically noted. However, when counting spaces for an ability, players cannot count spaces through a door because the spaces are not considered adjacent.Emphasis mine.
What I mean by the "yes" part, however, is that after you have chosen a valid target within three spaces of you, all other monsters in that group are Stunned, whether they are behind a door or not.