Adult Swim has built up a nice stable of games on the App Store, and the biggest workhorse in it is Robot Unicorn Attack, a Flash game that's an endless runner where you play as the titular creature dashing and jumping to '80s music playing in the background. That game's been very successful, but due to the music licensing, Adult Swim's never been able to turn it freemium, which is a business model that potentially offers a bigger audience (and more profits).
Robot Unicorn Attack 2, however, is built freemium from the ground up. It's free to download, and the game earns you a currency which you can spend on powering up your unicorn, customizing it with various extra items, buying boosts to help your score and so on. The music has changed to something a little more easily licensed, though you can still buy a number of real licensed songs (Corey Hart!) via in-app purchase. And while there's not multiplayer per se, there are also daily and weekly challenges, designed to get you to beat your own high score, or fight for your faction in a larger competition.
The game itself hasn't changed much, though the boosts and the upgrades do pack a pretty solid punch (you can add plenty of extra jumps to your unicorn's repertoire, and even fly once you've reached full speed). Developer PikPok (best known for their great Monsters Ate My Condo games) has done an excellent job here riffing on the original title, while still keeping Adult Swim's freemium requirements in place. Robot Unicorn Attack 2 is definitely worth a download -- the freemium elements aren't always successful, but this is a solid update on Adult Swim's most charming game.