, Chewii doesn't meant that with underground.For the underground, you can make another "mirror" underground map, and trigger it so that if you say, dig underground, your unit is moved to the underground part of the map (e.g. unit casts ability (dig), as long as in diggable region, move unit x down). My explanation is really bad, but that concept is used in the game "water war" - which is an amazing aos game. For other things like abilities, it will be a lot more difficult to do.