For the best (and safest) experience, search for the format of the game. The file name should be something like New Super Mario Bros. Wii (USA) (En,Fr,Es).rvz . Verify the MD5 checksum online to ensure it’s a clean dump.
Start at 1x (480p). If your phone stays at full speed, try 2x (720p) for much crisper visuals. For the best (and safest) experience, search for