Instant, 2U (3)
Common
Counter target spell unless its controller pays {1}. That player discards a card.
Whether he actually exists is in question, but the terror she feels is excruciatingly real.
Illus. Anthony Palumbo

9/22/2011: You must target a spell in order to cast Frightful Delusion. You can't cast it without a legal target just to make a player discard a card.
9/22/2011: The player discards a card even if he or she pays {1}.
Legal in Vintage (Type 1)
Legal in Legacy (Type 1.5)
Legal in Extended (Type 1.X)
Legal in Standard (Type 2)
Legal in Classic (MTGO)
Legal in Commander
Legal in Modern