Hardened Scales is a rare Enchantment card from Khans of Tarkir Promos (PKTK), collector number 133p. Current market price: $4.27 (foil $5.09), TCGplayer market prices via Scryfall.
If one or more +1/+1 counters would be put on a creature you control, that many plus one +1/+1 counters are put on it instead.