Enable root for your NOX first, then install Lucky Patcher. Go to ToolBox Menu in the LP and click on Patch to Andriod. In the following window, just tick everything and patch. Wait a bit then volia!
After that, install the game from google play store and let it run for a bit and install data. After finish, exit the app (DO NOT UNINSTALL IT). Go to this post on the browser in NOX and download the modded apk. Install the apk on top of the original apk and you're done!
Note: If you don't want to get banned (think its possible), don't use the modded app on stuff like arena and multiplayer. You should be fine with Devil's Tower and Field of Glory.
@BTG New update has been released. Could you update this mod when you got the time to do so? Thanks in advance.
Use increased damage. This happens when you try to fight another team of heroes, whose health is stored at server instead of your phone. So the only roundabout way is to use increased damage.