`special=true` is required for _Vanguard_. Compare the following:

  - http://gatherer.wizards.com/Pages/Search/Default.aspx?output=spoiler&set=[%22Vanguard%22]
  - http://gatherer.wizards.com/Pages/Search/Default.aspx?output=spoiler&set=[%22Vanguard%22]&special=true