Plunderer's Prize is a rare Sorcery card from Alchemy: Ixalan (YLCI), collector number 8.
Seek a nonland artifact card with mana value X or less and put it onto the battlefield. If a card with mana value less than X is put onto the battlefield this way, this spell perpetually gains "This spell costs {1} more to cast," then return this spell to its owner's hand.