Pocket Gamer Silver Award-winning retro platformer 1-bit Ninja contains a hidden feature that isn't included in the game's App Store description: level modding.
The latest version of Kode80's platformer features base maps for every level the game has to offer, as well as the respective levels' tileset and a handy level-modding guide - all of which can be obtained by plugging your device into iTunes and heading over to the File Sharing area.
To craft your own stages, you'll have to download Tiled Map Editor from its website, but this step - and everything else you need to know - is explained in the video below.
Once you've created your level, you can load it back into the game through the File Sharing area inside iTunes, and play it until your heart's content. Or something.
Check out the video below, which shows you the whole process. 1-bit Ninja is available on the App Store for £1.49 / $1.99.