>>37511244As the designs of Pokémon are usually one the first stage of development, Keldeo was most likely designed in around 2007/08. And besides, BW were released in September 2010, just before FiM started and bronies became a thing.
Maybe it's based on My Little Pony (the toy), who knows? But it's certainly not pandering to bronies, who didn't exist at the time BW were released.
