The Magic Mirror is a mythic Legendary Artifact card from Throne of Eldraine Promos (PELD), collector number 51p. Current market price: $4.71 (foil $4.03), 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.