Your browser does not support grid, so will not be supported. Hover over your browser version to see if there is a way to enable potential support. Sorry, I am no longer able to justify working on making the layout work on older devices.
I think "original form" has some pixiv-specific slang meaning, but I'm not really sure. Probably something to do with being the same style as the official Pokémon, i.e. not having genitals or any other extras an artist might otherwise add.