Fiend Artisan is a mythic Creature — Nightmare card from Ikoria: Lair of Behemoths Promos (PIKO), collector number 220p. Current market price: $4.65 (foil $4.93), TCGplayer market prices via Scryfall.
This creature gets +1/+1 for each creature card in your graveyard. {X}{B/G}, {T}, Sacrifice another creature: Search your library for a creature card with mana value X or less, put it onto the battlefield, then shuffle. Activate only as a sorcery.