Dresses are perhaps not the best choice for pony riding, especially if you refuse to ride side-saddle. But if you insist on wearing them in the name of festive fashion, be prepared for some uncomfortableness.
For this minstrel and pony, it is a festival all year round, and sometimes all night long.
Here is a good way to ensure you need a change of clothes.
Hat: Balladeer’s Hat, Moria barter, sea blue dye
Shoulders: Shoulders of the Might Verse, Moria barter, sea blue dye
Chest: Gossamer dress, skirm barter
Cloak: Cloak of the Dove, Store, sea blue
Pony: The Anniversary Mount was earnable at the festivals for the 4th and 5th LOTRO anniversaries. If you missed it, it will probably be available as a store mount next anniversary festival, if Turbine’s current trend of putting old festival mounts in the store holds.