The Magic Mirror is a mythic Legendary Artifact card from Throne of Eldraine (ELD), collector number 345. Current market price: $5.30 (foil $10.35), TCGplayer market prices via Scryfall.
This spell costs {1} less to cast for each instant and sorcery card in your graveyard. You have no maximum hand size. At the beginning of your upkeep, put a knowledge counter on The Magic Mirror, then draw a card for each knowledge counter on The Magic Mirror.