Fiend Artisan
Creature — Nightmare
This creature gets +1/+1 for each creature card in your graveyard.
, 
, 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.
Yigit Koroglu
Rulings
If a card in a player's library has {X} in its mana cost, X is considered to be 0.
(wotc • 2020-04-17)
Because damage remains marked on a creature until the damage is removed as the turn ends, nonlethal damage dealt to Fiend Artisan may become lethal if creature cards leave your graveyard during that turn.
(wotc • 2020-04-17)
Fiend Artisan's first ability applies only while it's on the battlefield.
(wotc • 2020-04-17)
Rulings
If a card in a player's library has {X} in its mana cost, X is considered to be 0.
(wotc • 2020-04-17)
Because damage remains marked on a creature until the damage is removed as the turn ends, nonlethal damage dealt to Fiend Artisan may become lethal if creature cards leave your graveyard during that turn.
(wotc • 2020-04-17)
Fiend Artisan's first ability applies only while it's on the battlefield.
(wotc • 2020-04-17)