Proft's Eidetic Memory is a rare Legendary Enchantment card from Murders at Karlov Manor (MKM), collector number 67. Current market price: $3.29 (foil $3.70), TCGplayer market prices via Scryfall.
When Proft's Eidetic Memory enters, draw a card. You have no maximum hand size. At the beginning of combat on your turn, if you've drawn more than one card this turn, put X +1/+1 counters on target creature you control, where X is the number of cards you've drawn this turn minus one.