Tablet of the Guilds is a uncommon Artifact card from Return to Ravnica (RTR), collector number 235. Current market price: $0.33 (foil $9.52), TCGplayer market prices via Scryfall.
As this artifact enters, choose two colors. Whenever you cast a spell, if it's at least one of the chosen colors, you gain 1 life for each of the chosen colors it is.