Discarding Portals

[Nixel]

Since that is not placing the portal card into play, you would not get a replacement card.

When you draw a Portal face DOWN, you have a choice:
(1) Turn it face up immediately and follow its instructions. After you
follow the instructions, draw another face-DOWN Door.
(2) Put it in your hand. You may play it later, but only if (a) it is your
turn, (b) you are not in combat, and (c) you haven’t already played a
Portal on that turn. When you play it, follow its instructions and immediately
draw a face-DOWN Door.