The Flavormancer is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Before the game begins, if The Flavormancer is your commander, legendary creature and planeswalker cards in your deck that are flavorfully Heroes or Villains gain that creature type. (For example, Gideon becomes a Hero and Yawgmoth becomes a Villain. Yes, planeswalkers get creature types this way. Don't worry about it.) Once during each of your turns, you may cast a Hero or Villain spell from your hand without paying its mana cost.