When do combat modifiers get discarded? (Also, Doppelganger question)

[Clipper]

The FAQ is specific that the cards are not discarded until the battle is over:

Originally Posted by FAQ

Q. When does a card move from play to discard? For example, if I use a one-shot Item during combat, is it in play during the entire combat or does it immediately move to the discards?
A. The one-shot card does not move to the discards until the battle is over. However, you no longer "own" that card, unless someone plays something to reboot the combat and return all cards to their owners, in which case you resume ownership.

So yeah, you can't use the same Doppleganger twice in the same combat. I can't think of any effect that would allow you to use the card twice in the same combat either, but if you were blending the deck with another set that had a card with the same effect as Doppleganger (such a card may not exist) or you did find a way to use the card twice in the same combat, then you would be able to use them together to quadruple your combat strength as your Doppleganger does not count as help.

Note: Do not use this post as fact. Double Dopplegangers are possible with a Fairy Dust card and they would triple your bonus, despite the card text saying otherwise. See posts below.