Happy from Fairy Tail and Pinkie Pie from My Little Pony. Happy is a fun - loving and friendly cat - like creature, and Pinkie Pie is the life of the party. They would likely find each other immediately and start having a great time together, sharing jokes and treats. Pinkie Pie might even teach Happy some of her party - planning skills.
Well, it could be Twilight Sparkle and Spongebob. Twilight is the intelligent and studious one in My Little Pony. She would be intrigued by Spongebob, who is clearly a very different kind of creature from Equestria. Spongebob, on the other hand, would be in awe of Twilight's magic and knowledge. Their first meeting might happen when Spongebob is exploring the library in Ponyville that Twilight often frequents. She would start asking him questions about where he came from and what his world is like.
Probably Naruto and Twilight Sparkle. Twilight is the intelligent and curious one in the My Little Pony world, always eager to learn new things. Naruto, with his unique ninja abilities, would be something completely new for her. She would likely approach Naruto first to find out more about him.
Probably Spongebob and Twilight Sparkle. Spongebob is always curious and eager to explore new things, and Twilight is the most studious and open - minded of the ponies. So when Spongebob arrives in Equestria, Twilight would be the one most likely to approach him first, wanting to learn about this strange new creature. And Spongebob would be happy to talk to her because she seems friendly and intelligent.
I think Pikachu and Fluttershy would be likely to interact first. Pikachu is curious and friendly, and Fluttershy is gentle and kind - hearted. Their personalities would make them approach each other easily.
Probably Goku and Twilight Sparkle. Twilight is the smart and curious one. She would be the first to approach Goku out of scientific interest, wanting to understand where he came from and what his powers are all about.
Natsu would be a likely candidate. He's always up for a challenge and not afraid to take on powerful opponents. He'd probably be the first to rush towards Godzilla, either to fight it or try to befriend it in his own Natsu - like way.
Sonic and Natsu would be likely to interact first. Natsu is always eager for a challenge and when he sees Sonic's speed, he would be intrigued and want to test himself against Sonic.
Gray is another candidate. Gray's cool and collected demeanor could contrast with Tobi's more mysterious nature. They could get into arguments about the best way to handle a situation, like when facing a powerful enemy. Or, they could find common ground in their skills and work together to protect Fairy Tail from danger.
It could be Zane from Ninjago and Trixie from Slugterra. Zane is very logical and has a lot of knowledge about technology and combat strategies. Trixie is smart and resourceful in the world of Slugterra. They might cross paths while investigating some strange occurrences that seem to be related to the crossover. Their initial meeting would probably involve a lot of questions and mutual curiosity as they try to figure out where the other is from and what they are doing in this new, combined situation.
Mercy from Overwatch and the Medic from TF2 could be the first to interact. Given their roles as healers, they would likely be interested in each other's medical techniques. They might start by comparing notes on how to heal their comrades more effectively, and this could lead to a deeper understanding and cooperation between the two groups.