I don't know there is a mod for the games that you said(maybe high value games so people doesn't want to release) but i guess you can mod Street fighter: Duel, since it contains client-side functions. Which feature u need?
If you want to damage hack, u need to find out where damage is stored; if you want to defence hack, u need to find out where defence stored... as far as it goes.
If stats are limited from server-side, probably there is nothing you can do; so you need to look for other exploitable values. Do you know how android works? What is your knowledge on tools and programming languages? How about your networking skills?
apk-tool, jadx, frida... these are some of tools you need while hacking apk, might be need some other tools but these are most common tools for hacking. Download Genymotion, build a Android phone and start using adb(android debug bridge) for communicating with other tools.
I'm interested in android lately, so if u want to discuss feel free to PM me. Maybe i will download Street fighter and investigate it for improving my skills.