Counting cards

You magically enchant cards to take the focus and ire of your attackers. The cards land in a 20 feet square that you choose. The creatures inside must make a Wisdom saving throw, failing would result in the creatures no being able to leave the square until the cards were either picked up or destroyed. Every round affected creatures can spend their action rolling 1d20 adding their dexterity modifier and picking up as many cards equal to the result. If the creature refuses to pick up the cards, they take 2d4 physic damage and have disadvantage on attack rolls.