The Disciple of Vess is a rare Legendary Creature — Human Cleric card from Unknown Event (UNK), collector number RB54. Current market price: $39.99, TCGplayer market prices via Scryfall.
Whenever The Disciple of Vess attacks, you may put a planeswalker card from your hand onto the battlefield. If you don't, create a token that's a copy of a Liliana planeswalker chosen at random. (There are currently thirteen. Perhaps look up the list and roll a D20?)