Part 1: http://www.welivesecurity.com/la-es/2016/12/19/analizar-apk-con-mobsf/ Part2: http://www.welivesecurity.com/la-es/2016/12/21/analizar-archivos-apk-mobsf-parte-2/
Backdoor-apk, it's a script in bash, writed by Dana James, this make easy the process to add a backdoor to any file APK of Android. You need to have practical knowledge of Linux, Metasploit, Apkool, SDK de Android, smali, etc. The code is here:
You'll find the APK recompiled in directory "original/dist", Then install the APK on any compatible device Android, run and and handle the connection meterpreter through the script resources : msfconsole -r backdoor-apk.rc