[MunchkinMan]

Rather than opinions, I'll give you official statements of fact. :-)

First off, Doppleganger can only be played when there is only one player in combat; your Level 9 Elf could not have played it. Secondly, if they already had defeated the Monster, you couldn't have played this mystery potion unless it says you can play it even after the Monster(s) have been defeated. If you mean to say that they were going to win the combat, that's a different story. Regardless of all that, they weren't winning because Doppleganger was an illegal play.

I'm assuming, actually, that you are referring to Friendship Potion, now that I've had a chance to look at the database. And, no Treasure is gained, since this is what the card says. The charmed Monster's Treasure is lost to the munchkins as well. If we wanted to say otherwise, it would be documented in the rules or the card that Monsters, defeated in such a way that gives Treasure prior to a card being played that would remove any remaining Monsters and their Treasure, would still give up their Treasure at the end of the combat (do you see how confusing a statement that is?). Neither Friendship Potion nor the rules say this, so no Treasure.