First you teleport to the event.
Once there you look at each of the designers items they have out.
MOoH! has made an exclusive item just for the event.
Now you have a choice to make, You can either buy it there OR if you want a big discount on that item you can grab a LM and hint at each of their vendor spots, the landmarks will take you to the main store or a place you need to hunt to find the PURPLE FLOWER, When you find this flower, Buy it for the bigger sale price and then its yours.
This dress will be 125L at the event site and only 75L at the main store. The choice is yours!