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.

'[#[Links]
'[l[http://en.wikipedia.org/wiki/Pixel_art[Wikipedia's explanation]
'[l[http://www.pixeljoint.com/[Pixel Joint] is an online competitive pixel art community
'[l[http://en.wikipedia.org/wiki/List_of_8-bit_computer_hardware_palettes[Wikipedia's guide to classic computer palettes]
'[l[http://en.wikipedia.org/wiki/List_of_videogame_consoles_palettes[Wikipedia's guide to classic vg console palettes]