To pass challenge 4 (the one with the dragon, sword, and shield), have your shield follow your sword, and move tangentially around the dragon, trying to keep your shield closer to the dragon, but not in your sword's line of fire to the dragon. It may take a bit of luck and a few tries, but this strategy will work. The dragon will target whichever of your bots is closest (assuming your bots are not too close, in which case the dragon will target whichever bot is in range).
you will only move your sword once your shield is locked onto and following your sword.
 "Spewer"){kind=icon}
 "Open Doors 2"){kind=icon}
 "Bureau of Steam Engineering"){kind=icon}
 "Casual Gameplay Escape"){kind=icon}
 "Super Energy Apocalypse : RECYCLED!"){kind=icon}
 "Chronotron"){kind=icon}
 "Bot Arena 3"){kind=icon}
 "Pyro"){kind=icon}
 "Pandemic 2"){kind=icon}
 "Face"){kind=icon}