Hi there! Toromak here, and this is a quick tutorial on how to import pixel art into Unity3D.
First, you have to save your pixel art into your project's assets folder (preferably within a subfolder called Sprites or something). I highly recommend using the PNG format. NEVER SAVE PIXEL ART IN JPG OR GIF FORMATS. These formats compress the art and ruin the crispness of pixel art. When you first import the sprite, it will be very blurry. It is simple to change this. Simply click on the image on the side panel of Unity, and the Import Settings will appear on the right side. Just change the Filter Mode to point, (which will preserve the sharpness) and the Format to truecolor, which will keep your beautiful pixel art colors. Remember to hit apply before leaving to work on your amazing pixel-y game!