i just hacked the achievements file. so i don't know. i tried exploring priate bases, like aformentioned, but i never found it. i even made a custom map with 9 undefended pirate bases, and none had the ponies. so i got tired and just edited the achievements file for it, and all the other achievements. i didn't get any secret mod, nor did i get an explaination of the ponies achievement. take my advice, and give up the search. leave the ponies alone, and let them be free.