Fiend Artisan is a mythic Creature — Nightmare card from Magic Online Promos (PRM), collector number 80855.
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.