Pixel is for pixel art, either animated or not. Typically each pixel is placed one at a time using a pencil tool. Large pixel art can take days, weeks, even months depending on how many time-outs an artist takes from a project.
The rules for a pixel OHB may or may not include a palette and/or size restriction. Even if a size restriction is not included in a battle's rules, it's a good thing to consider. The 8-bit era saw a lot of resolutions around 320x200, but these did not have square pixels. The PC's VGA had a hacky thing called x-mode that demo scene programmers found by manipulating the refresh rate, achieving 320x240 which has a 4:3 ratio and a square pixel.
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