Riptide Pilferer is a uncommon Creature — Merfolk Rogue card from Planar Chaos (PLC), collector number 60. Current market price: $0.13 (foil $4.38), TCGplayer market prices via Scryfall.
Whenever this creature deals combat damage to a player, that player discards a card. Morph {U} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its morph cost.)