I'm just going to put the bug exploit tutorial here if people just want to try it.
Step One: Stop masturbating, wash your hands, and take your iPad/Pod/Phone.
Step Two: Open Knights & Dragons.
Step Three: After everything loaded go to Arena.
Step Four: Battle someone, if you lose, redo this step until you win.
Step Five: Win, Double Down.
Step Six: Battle someone else.
Step Seven: As you battle this person, estimate your chances of winning or losing.
Step Eight: When you feel like you're about to lose press the cross on the top of your screen to pause the game.
Step Nine: Press your home button and wait to get out of the game.
Step Ten: Double click your Home button and close the Knights & Dragons app.
Step Eleven: Re-Open Knights & Dragons.
Step Twelve: Once everything is loaded, go back Arena and repeat from step Three to step Twelve.
Step Thirteen: Once you run out of Energy, click Double Down, it will ask you to either Retreive Reward or to Get Energy. Press get energy, leave this menu and you're done. Wait about an hour before returning to your phone to repeat this process.
Voila, you exploited the PVP bug and you'll be able to Max your double downs.
WARNING: DO NOT WAIT UNTIL THE LAST HIT OF YOUR OPPONENT, IF HE HIT'S YOU, YOU WILL NOT BE ABLE TO HIT THE CROSS AND YOU WILL LOSE YOUR DOUBLE DOWN
How this works: Gree thinks your game just crashed, so it doesn't penalize your double down. It does however remove you an Arena Energy, but you don't care, because you'll win over 200 Arena points once your done.