Using an emulator (Bluestacks running in Windows), you can target the process HD-Player.exe, and get the olde Cheat Engine do its job.

Most stuff is 1x4Bytes, and where multiple entries appear, change them all.
Example variables to modify/freeze: HP, attack, boss HP, stage gold (capped at 7400).

Not much depth as a game imho, but it was fun exploring and exploiting around.