Hidden Stockpile is a uncommon Enchantment card from Aether Revolt (AER), collector number 129. Current market price: $0.27 (foil $1.15), TCGplayer market prices via Scryfall.
Revolt — At the beginning of your end step, if a permanent left the battlefield under your control this turn, create a 1/1 colorless Servo artifact creature token. {1}, Sacrifice a creature: Scry 1.