"What is a pony?" is the title of the opening game window, seen briefly after the player runs Ponyvania: Order of Equestria and while the game is loading. Another Castlevania reference, this quote is a truncated parody of "What is a man? A miserable little pile of secrets!", the oft-quoted line bombastically said by Dracula during the Prologue stage to Castlevania: Symphony of the Night. Dracula's line is itself a quote from André Malraux's Antimémoires, published in 1967. The quote is therefore an anachronism, as the events of Castlevania: Symphony of the Night take place in the year 1797, 170 years before the writing and publishing of Antimémoires.
Naturally, as Equestria exists outside our own reality -- while the Castlevania series exists within our reality, albeit an altered form of it -- the laws of our reality, including anachronism and other temporal restraints, do not necessarily apply to ponies and their quotes.