The pixel art itself was done in GIMP using lots and lots of layers, similar to how the original Paper Mario: TTYD did it on the GameCube.

I created the hands by drawing one vertical hand, rotating it with the default rotation tool set to no interpolation, and then traced the newly-rotated hand. I then flipped the hand around and mirrored it to the other side.

I applied shadows to most objects by cloning them, filling the entire layer with gray, and deleting anything that wasn't in the white area of the object which the shadows were being cast on.

The resulting piece:

Now all that was left to do is scale it up around 8x it's normal size if I remember correctly, which was literally a 1-step process. You can check out the final artwork soon on my art page!