DroidFrida is an android app for executing frida scripts directly on your android device. Frida is a dynamic instrumentation framework that allows to edit memory and hook methods, which is very useful when analyzing and cracking application (including games). Frida gives large posibilities, and I use it very often, so I created an app to use it easily.
You will need root access (or vphone) on your phone otherwise this won't work. Enter the package name of the target application as the -f flag and input your script in the text field. You will be able to run target app with the frida injection.
You can find documentation for frida javascript api here.