(twi|pony)booru.org

4) Images of a pony sitting or standing on all fours should be a minimum of 800px in height, head-to-hoof. 1200px is preferred. Images of ponies standing on their hind legs or in an unusual pose should be proportional.

The pony is too small to be included in the collab. Standing/sitting ponies have to be at least 800 pixels tall and other poses proportional; this puts the requirement for bipedal ponies at around 1000 pixels tall. No, adding blank space won't work.