How do I set an animated desktop background without OnyX?
Yes, this can be done without OnyX.


  First head to System Preferences > Desktop &amp; Screen Saver > Screen
  Saver and select one of the screen savers included in OS X, or a
  third party screen saver that you’ve previously installed. Whichever
  one you choose, just make sure it’s selected as the active screen
  saver, even if you have it set to never start in the “Start After”
  duration drop-down menu.
  
  Next, launch Terminal (located in the Applications > Utilities
  folder), copy and paste the following command, and press the Return
  key on your keyboard to execute it:

/System/Library/Frameworks/ScreenSaver.framework/Resources/ScreenSaverEngine.app/Contents/MacOS/ScreenSaverEngine -background



Source: How to Set a Screen Saver as the Desktop Background in Mac OS X