Sphinx's Herald

• WWizards of the Coast2008-10-01
  Official Ruling
  To activate the ability, you must sacrifice three different creatures. You can’t sacrifice just one three-colored creature, for example.
• WWizards of the Coast2008-10-01
  Official Ruling
  You may sacrifice the Herald itself to help pay for the cost of its ability.
• WWizards of the Coast2008-10-01
  Official Ruling
  You may sacrifice multicolored creatures as part of the cost of the search ability. If you sacrifice a multicolored creature this way, specify which part of the cost that creature is satisfying.
• WWizards of the Coast2008-10-01
  Official Ruling
  The only difference between a colored artifact and a colorless artifact is, obviously, its color. Unlike most artifacts, a colored artifact requires colored mana to cast. Also unlike most artifacts, a colored artifact has a color in all zones. It will interact with cards that care about color. Other than that, a colored artifact behaves just like any other artifact. It will interact as normal with any card that cares about artifacts, such as Shatter or Arcbound Ravager.

Rulings via Scryfall