This is a guide on how to install Ygopro on Android.
Android 4.1 - 6.0
Internal storage at least 300MB free.
~25MB for the apk, ~250MB for card images and other assets
Display at least 480x320
The latest version can always be found at the download page. The first link is the Ygopro APK file. The APK file installs the app. If you are doing a clean install (meaning you don't have an older version of Ygopro installed on your device yet) then you also need to download the Android card pics.
Ygopro is a big app. The card images take about 250MB of storage space. To avoid having to download the images for every update they are not in the stored in the main APK file, but in separate OBB files.
The OBB files need to be placed in a specific folder on your device internal storage (SD card on older devices). The app searches for them in 2 different locations.
Connect your device to a computer via a USB cable. Browse to one of the folder locations (your choice). If the folder does not exists, then create it manually. Copying to only one of those folders is enough. You don't need to copy the OBB files to both folders. You end up with this:
You only need to copy the main OBB file once! Only the APK and patch obb files are needed for installing updates.
The device needs to allow installing from a source other than the official Google Play store. This is called sideloading.
With this done, you can put that APK file on your phone by connecting your device to a computer via a USB cable. You can also download the APK straight from the Ygopro website by scanning the QR code on the download page. (I recommend Barcode Scanner)
Using a file manager application (I recommend ES File Explorer), find the Ygopro APK file and tap on it. You’ll see what permissions are required, and the ‘Install’ button at the bottom.
After installing you can start the app by tapping on the duel disc icon.