(aka Twice As Fancy Ponies)
As a child, my conscious memory with this set was of a change - a move away from the old styles and designs I was used to and into a brand new wave of My Little Pony ideas. I think this was partly to do with the fact that they were one of the first UK sets to feature a new style of packaging - with a coloured border around the rim and the ponies pictured inside it (see below, scan courtesy of Lady Guinevere!). They also featured a different design of insert, and no longer came with round puffy stickers - which earlier UK-sold 1987 sets still retained. The Party Ponies were one of the first sets also to not figure in the Fact File.
STRAWBERRY FAIR's BACKCARD (1987, UK)
The set were called "Party Ponies" in the UK, a name adopted also in the European countries which used the same basic set design (I have Lollipop on a German card, but the style is basically the same). In North America, they were known as "Twice as Fancy Ponies", a label I generally adopt because it encompasses all the ponies sold in this style over two years - the term "Party Pony" only refers directly to these six new characters. Some of the set also had different names in the North American release.
The gimmick that these ponies put out is obvious from the first glance. Instead of neat symbols in the usual location, they had patterns spread out across their sides and over their back, making them literally "twice as fancy" as the other ponies in the range. They also all had a little interpretation of their symbol on their cheek or nose, and this is a good way of distinguishing them from other later sets who use similar symbol style techniques. Despite this new look, however, the basic rules of pony design were still in place. The only unicorn from the set - Milky Way - had a typical coloured streak in her mane to mark out her species, whilst the others had simple, single coloured manes and tails.
Milky Way also came with a variation - see her page for more on that subject!