it would be cool if there was a pixel filter
Viewing post in Plants Vs Zombies DS comments
essentially, it just makes it so that things always look pixelated, rather than, as an example, when the zombie's head falls off the pixels rotating, they stay the same direction, while the head rotates, mimicking the way that the game used a console that had the zombies pixel-accurate.
(as an example, download shaderglass and set the shader to 'none'.)