Form of the Stax Player is a rare Enchantment card from Unknown Event (UNK), collector number RW05b. Current market price: $30.30, TCGplayer market prices via Scryfall.
At the beginning of your upkeep, create a random token that's a copy of one of the following: Aven Mindcensor, Drannith Magistrate, Ghostly Prison, Hushbringer, Smokestack, or Thalia, Guardian of Thraben. (There are six of them, so one easy way to select is to roll a D6.) When Form of the Stax Player leaves the battlefield, sacrifice each token created with it.