How does the swap door work?

Question

I know items dropped on the door are swapped out for another in the next turn, but is that swapped item gone forever or will it reappear on a later restock?

Also, can I swap items when the door is empty (shows "0")? Will it replace or just destroy the item?

Answer 1

Items swapped out through the door will reappear later.

The best analogy is the bag of tiles in a scrabble game. There is a fixed quantity of each piece. (Incidentally, being aware of these fixed unit counts can be very helpful in forming strategies. Knowing a Council opponent is out of wizards and fireballs allows you to clump more freely to counter knights for example.) Placing one from your hand back into the bag does not eliminate it from future play.

You cannot swap at 0 reserves.