Trained on the pixel art character icons from the Nintendo / Square Enix crossover game Mario Hoops 3-on-3 (2006) for the DS.

The images aren't quite a square aspect ratio. I recommend generating at 768 x 704, then using something like Pixel Snapper to align the pixels to a grid better. An upscale/hi-res pass can improve details, but can also throw off the last step with inconsistent pixel sizes.

This is the node I ended up using in ComfyUI to fix up the pixel art: https://github.com/x0x0b/ComfyUI-spritefusion-pixel-snapper