The Guardians weren't the first spirits Jack had encountered in his existence as a winter spirit. In fact, some of his them - who were now his friends - had been around for longer than the Guardians themselves.
(This excluded very ancient entities, like the Wind he danced with daily or the Ocean that waved to him as he flew above its waters. While he was fairly sure they could take a form if they so desired, he had not had such an meeting with them yet.)
For instance, during the first few months he spread winter around the world, he had accidently drifted too far south - which isn't to say he never went south of the equator, of course he did, they got winter down there too. But the Pacific islands weren't supposed to get a foot of snow during the middle of July (although Hawaii did get a good amount in the winter months).
His slip-up was bad enough for the people and environment that other spirits had been required to reverse its effects. He wasn't entirely sure they were spirits, though; the larger one adamantly called himself a demigod. (Jack was inclined to believe it after the small figure on the person's chest waved at him in greeting).
Maui, shape shifter, demigod of the Wind and Seas, Hero of All, he'd introduced himself as, proudly lifting his giant fishhook. It made Jack's wooden staff seem small in comparison. The intimidating factor didn't seem to be working full force though, because Maui was shivering in all the snow.
The other being was a lot friendlier to him from the start. "Don't worry about it, Jack! We all make mistakes." She leaned in conspiratorially and added in a loud whisper, "at least you didn't almost destroy the world."
Maui groaned and crossed his arms. "It was only one time, and I helped fix it too!"
Somewhere in the midst of hearing about their first adventure, he learned that this mischievous woman was Moana, protector of Te Fiti, demigoddess of the Islands and Seas. "The Ocean insisted that we share the title," she explained.
"Seven oceans for two of you seems alright," Jack agreed, drawing grins from both 'demigods.' Silently, he was planning his own title. It made them seem more… legendary. He supposed he was legendary in that area of the planet now anyways, or at least what he had caused was.
Even though the warm weather was slightly uncomfortable, Jack wished he could stay with the pair for a while. He didn't have any friends; his task meant he was constantly on the move and annoying other spirits with the cold he brought. Besides, the Moon hadn't granted him a partner either, and he was lonely. His tropical mishap was a blessing in disguise, if only for a short time.
Looking back on his first visit, he realized its effects lasted longer than expected. Decades later, he still carried around a sand dollar in his sweater pocket given to him by Maui and Moana.
(The same could be said for the other side of the equation, as when he did run into the demigods again, Jack found himself being scolded royally for not ever stopping by. A vexed demigoddess Moana was far scarier then Pitch ever was.)
This is an expansion into the Disney and Dreamworks universes, but didn't really fit into any one crossover section (and it is Jack-centric). This will be continued!