Whammy Burn is a rare Instant card from Mystery Booster Playtest Cards 2019 (CMB1), collector number 70. Current market price: $0.27, TCGplayer market prices via Scryfall.
Shuffle your whammy deck, then reveal cards from the top of your whammy deck until you reveal an Island or choose to stop. Then, if no Islands were revealed this way, Whammy Burn deals X damage to any target, where X is the number of cards revealed. (A whammy deck consists of a Plains, Island, Swamp, Mountain, and Forest.)