Winter Wishday has arrived in Maretime Bay, and Sunny is eager to celebrate it with her friends for the first time. However, Hitch had promised to celebrate it with his Grandma Figgy, Izzy wants to celebrate Wishiehoof by going to Bridlewood and hanging an ornament on the wishing tree, and Pipp and Zipp have a royal obligation to perform in a concert to celebrate Wishentine. Not wanting to interfere with any of those plans, Sunny agrees for everyone to attend all of those celebrations before returning home in time to watch the Wishing Star. Visiting all those distant places in a single day seems impossible, until Izzy and Zipp decide to reveal a secret project they've been working on, which is converting an old tram car into a flying vehicle, and while it doesn't look like much at first, Sunny's magic lantern suddenly transforms it into a very spectacular vehicle that resembles an RV with wings, which Izzy decides to call the Marestream.
Despite what is apparently the first snowfall the coastal town of Maretime Bay has ever seen, the main ponies fly in the Marestream to their first destination, which is Grandma Figgy's house. Hitch explains to his friends that his grandma always wants everything done in a particular way for the holiday, but once they meet her, it quickly becomes clear that it's actually Hitch who insists on following the exact same holiday tradition, and that Grandma Figgy actually welcomes some changes, though the others are respectful enough to Hitch to play along with the traditions (while also doing some new things when he's not paying attention). After enjoying some hot cocoa, looking through a few photo albums, and building some gingerbread houses, the main ponies say goodbye to Grandma Figgy (who also allows Zipp to borrow a book about ancient holiday legends) and depart in the Marestream.
They next arrive in Bridlewood, and after Izzy provides everyone with scarves to protect against the colder than usual weather, they head to the Wishing Tree, where the unicorns each hang an ornament to supposedly ward off any misfortune. Despite her friends running on a tight schedule, Izzy takes some time to greet many of the other unicorns, using the traditional holiday greeting of "Frosty Feelings". Even after Izzy finally gets around to hanging her ornament, she's so pleased to see everyone that her friends practically have to drag her away just so they can leave on time.
After a terrifying flight through a blizzard to reach Zephyr Heights, Pipp gives some VIP tickets to the others so they can relax in a special suite at the theater before the royal Wishentine concert, while Pipp and Zipp follow their holiday tradition of window shopping with their mom, Queen Haven. After a while, it's time for the concert performance, and Zipp and Pipp (and their friends) are shocked to discover that it's been expanded to six acts. Once the royal performance is finally done, the main ponies try to rush back to the Marestream, but can't find it under the immense snowfall. They are soon able to find it, thanks to making a wish on Sunny's magic lantern, and once they climb inside, Zipp realizes that (according to the book she had borrowed) the blizzard is being caused by all the unicorns who are unaware their holiday greeting is actually a magic spell that brings cold weather.
To stop the blizzard, the main ponies rush back to Bridlewood and warn the now freezing unicorns about what they've been unknowingly unleashing. Izzy suggests changing the holiday greeting to "Warm Wishiehoof", and once enough unicorns start using it, the blizzard soon clears away. With that problem solved, the main ponies return to the Crystal Brighthouse just in time to watch the Wishing Star soar through the sky. Although none of them have any gifts to exchange, Sunny is just happy that they were all able to enjoy their holiday celebrations together.
First of all, I think it's fair to say that due to the three tribes being separate for a very long time, the old holiday known as Hearth's Warming (which celebrated the first unification of ponies) would have ended up forgotten, and in its place developed three different versions celebrated by each of the formerly separated tribes. The fact that some of the holiday songs even have the same melody but with different words would seem to indicate that. At Grandma Figgy's house, one moment that I found really notable was one of the photos we saw was when Sunny and her dad once celebrated Winter Wishday with Hitch and Figgy, which was really touching when you consider that Argyle is not around anymore. In Bridlewood, it was nice to see Alphabittle make his first appearance since the movie (not counting Tell Your Tale) along with that poet pony (who is apparently named Onyx), and that we apparently got to see some of those bunnycorn creatures (albeit quite different from how they're depicted in Tell Your Tale) as well. At Zephyr Heights, while I expected Zipp to dislike participating in the concert or wasting time with window shopping, I was quite surprised to see Pipp sharing the same feelings as well (I guess the urgency of going through all the other holiday celebrations in one day might've gotten to her). Some amusing things were the pegasus guards trying to pass off the decorative empty presents as containing clouds, and the concert running so long that almost everyone grew bored and tired by the end of it (except Queen Haven, who seemed to be the only one who remained enthusiastic the whole time). Finally, it should be noted that while we know unicorns are capable of many magic spells, we've thus far seen them only use levitation of objects, so this is virtually the first time that any of them became aware that their magic can do other incredible things, so it'll be interesting to see what other magic spells they might rediscover later on in the series.
Overall, a nice holiday special to close out the first year of new episodes, complete with a lesson in enjoying the holidays with friends and family regardless of how you celebrate them.