Yep. Game is broken. Change tabs as soon as you start a fight, wait for the sounds to stop, and when you go back to the tab, you'll have won the fight with no health lost. I went into the arena with 3M power and beat someone with 21M+ without losing a single point of HP this way.
 "Pacifish"){kind=icon}
 "Raid Heroes: Sword and Magic"){kind=icon}
 "Sort the Court!"){kind=icon}
 "Sushi Cat 2"){kind=icon}