This Wiki article reveals the secrets that can be unlocked in N v1.4. If you clicked on this article by accident and don't really want to know the HUGE secrets that N v1.4 has, you better not scroll down...
..continue reading if you're determined to be a big cheater..
...The unlockable secret after beating your sixth column is called 'overclock mode'. With this, you can change the game's speed. The only purpose of this feature is for the player to experiment and have fun. After beating all ten columns, you'll unlock an RGB slider that allows you to make the ninja any color you desire.