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.