13) What are portals: are they objects, walls, doors? Can they be destroyed? Are they part of the map? Do the open ends on the map not represented by portal markers count as portals themselves?
In the rules, portals are a specific type of indicator marker used to indicate adjacent squares. These markers are placed off the game board. As you cannot target anything off the game board, you cannot target a portal. They are not doors, or walls, and as per the rules they are not objects - because objects are all inanimate things (other than treasures) INSIDE the labyrinth. Portals are not inside the labyrinth... nor are things like stun tokens, hat tokens, magic cards for that matter.
The open ends on maps not represented by portal markers aren't portals, they are Wrap Arounds. Wrap Arounds take you from one sector to the other sector exactly opposite. Portals take you from one sector to an diagonal sector. Portals criss cross the map. Wrap arounds do not criss cross.
2) Boomstone says after use, discard Boomstone. Does this mean its dropped or destroyed? The second paragraph specifically states another instance that does destroy the Boomstone, so does discard and destroy mean two different things or the same?
I do not think discarded and destroyed are the same thing. There is a discard pile not a destroyed pile. So if you are to discard something it goes into the discard pile and it's corresponding object token gets taken off the game board and placed back in it's token pile. That means no one can pick it up at and use it till it comes out again. When there are no facedown magic cards to draw, the discard pile gets shuffled, which means there is a chance for the Boomstone to be used again.
I believe when something is destroyed, you must set it aside, out of the game altogether as it can no longer be a part of the game. The card cannot be reshuffled back in, the token cannot be used.