If one were attempting to design a game that could be described as "systemically addictive," it would be difficult to top the concepts found in Puzzle & Dragons. Players navigate a dungeon, taking part in battles, capturing monsters and using those monsters to battle other, more powerful monsters. In lieu of combat, all conflict in Puzzle & Dragons plays out on a grid full of icons which players must align to perform attacks. It's a simple system that's easy to learn but difficult to master, and Gung Ho is constantly adding new, free content to the game, including crossovers with other media properties like Batman, Hello Kitty (pictured above) and the stylized robots of the Evangelion anime.
If you're suddenly intrigued by the mobile game that's taken Japan by storm, you can find Puzzle & Dragons available on both the Android and iOS app stores. It's free-to-play, but know that the temptation to spend real-world cash on Magic Stones grows pretty intense after the first handful of dungeons.