Form of the Stax Player (RW05b) [Unknown Event]

At the beginning of your upkeep, create a 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.