Rules FAQ:

• Varys's Riddle doesn't copy an ability, it initiates it. When resolving Varys's Riddle, take the opponent's plot in your hand, and resolve its When Revealed ability as if you've just revealed that plot instead of Varys's Riddle.

• If one player reveals Summer Harvest and another player reveals Varys's Riddle, then the First Player (likely the one who revealed Varys's Riddle) can choose whether the gold value of Summer Harvest is 2 or 7. (More details)

• When you resolve the when revealed ability on another player's plot card, you're considered to be the controller of that plot card while it resolves, so characters that are "immune to opponents' plot effects" (e.g. Maester Luwin, Septa Mordane, Winterfell Heart Tree) will not be protected.

Rules FAQ

• Varys's Riddle can only initiate a "When revealed" ability on a currently revealed plot card (not a used plot).
• Varys's Riddle, like all "When Revealed" plot abilities, is not optional. You must do it even if the ability will be detrimental.
  • For example, if you initiate the ability on Trading with the Pentoshi, your opponent will gain 3 gold.
  • If you initiate the ability on your opponent's Power Behind the Throne plot, you have to put a stand token on his plot, because the ability on PBtT says to place the token on PBtT (by title).
• The interaction with Summer Harvest it tricky. See this thread for details: www.cardgamedb.com