If you execute a Drunk Disguised as a Knight, do you take 2 DMG 'coz it was a Drunk or 9 DMG 'coz the Knight was corrupted?
i believe by "fake" it means that Outcast will appear in the deck, but will never actually spawn. So a fake Doppelganger would mean it looks like Doppelganger has a chance to spawn, but it never will (and you don't know that)
