For this achievement you need to get a golden guardian.The way I did this is save up points until you can buy one of the higher priced guardian packs (or you can use cash to buy them) and you may or may not get a gold one I got one every 2nd time I bought the 5000 points one. To update I found out from 2 other gamers you can get this from the 500 points pack it's 100% random it seems.