Lucky Ponies were made by Meritus Industries and are marked 1997 M.I.I. MADE IN CHINA on the belly. They are about 3.75″ tall. More information has been compiled in this forum thread. Recently I was lucky enough to purchase a MIB Lucky Ponies Playset that lists 8 different sets. Additional ponies have been found.
Lucky Ponies Traveling Beauty Cart (2 versions, one treasure chest cart and one fold-out flowers like Princess of the Flowers):
Lucky Ponies Magic Show:
Lucky Ponies Circus Parade:
Others: