The Keeper of Favorite Cards is a rare Legendary Creature — Human Soldier card from Unknown Event (UNK), collector number RW90a. Current market price: $9.75, TCGplayer market prices via Scryfall.
Whenever The Keeper of Favorite Cards enters or attacks, choose a nonland card name and add it to your favorites list for this game. (You can have limitless favorites.) Your favorite creatures get +1/+0. Whenever you cast one of your favorite noncreature spells, create a 1/1 white Soldier creature token.