This is the most reliable method. You stream the actual game from a cloud server to your phone. You do not need to download large APK/OBB files, and you don't need a high-end phone.
Some players use emulators to run the console versions of the game on high-end Android devices: Call of Duty: Black Ops II call of duty black ops 2 apk obb for android verified
These are available on Google Play and are regularly updated and verified. This is the most reliable method