First launched back in 2013, Duet is an insanely popular game on both iOS and Android, with 50 million downloads on Android alone. The game was critically acclaimed upon release four years ago, and it's easy to see why. Everything from the presentation, the art design, the music, and the difficult-but-fair gameplay make this an excellent addition to your offline collection of games. As a challenging game for casual and hardcore gamers alike, Duet is one of the few games on this list destined to thrill, frustrate, and excite players of any capacity. Whether you're looking for a game that keeps you occupied for a few minutes or a few hours, Duet can fulfill that and so much more—it's one of the most difficult casual-style games we've seen on mobile platforms.
The graphics are simple and beautiful, with most of the gameplay taking place against a dark black background. You control two dots, one red and one blue, which rotate around each other in sync with one another, as you spin them one way and the other to change their location and dodge difficult obstacles and barriers. If you happen to hit a barrier, your dot explodes in a paint splatter that remains on the level in future retries, creating this beautiful sea of blue, red, black, and white. The game really shines through with its music, though, which resembles cold and distant trip-hop and techno, helping to create the desired atmosphere of energy and fast-paced movement, guiding you through a maze of rotating lines of destruction.
All of this makes for an experience that essentially represents the videogame equivalent of chugging an energy drink: it makes you jittery and a bit stir-crazy. This game oozes personality, but not without some tight gameplay too. Levels are presented in short, easy-to-accomplish goals, but with enough challenge that by the time level three rolls around, you'll be dying a lot before you move onto the next level. There are a couple flaws in Duet, however. First, ad breaks on the Android version (the iOS version is a paid $2.99) are way too long and happen way too often. Every few levels, the game will ask you to upgrade to the paid version of Duet, and if you refuse, a fifteen-to-thirty second, unskippable ad will begin to play. Obviously, we also wish the iOS version had a free tier, but nevertheless, both the Android and iOS versions of the game are more than worth the $2.99 entry fee for an ad-free experience.