Harry Potter himself would be likely to interact with Elsa. Given his own experiences with unique powers and his role as a hero, he would be sympathetic to Elsa's situation. They could bond over their shared sense of responsibility and their ability to do things that others can't. Harry could also introduce Elsa to his friends and the world of Hogwarts.
Black Widow could be the first to form a friendship with Elsa. Black Widow is very perceptive, and she would quickly realize that Elsa is not a threat but a potential ally. She has a way of getting close to people and making them feel comfortable. She could help Elsa adjust to the new and strange world of the Avengers, and they could bond over their shared experiences of being different from the rest of the group. Elsa's powers would also be something that Black Widow could see as a valuable asset in their missions.
I think Tooth Fairy would be the first. She is very kind - hearted and is always interested in new things. Elsa's unique ice powers and her beautiful ice creations would draw Tooth Fairy's attention, and she would be eager to make friends with Elsa.
Hermione would likely be very curious. She'd want to research all about Elsa and how her powers work in relation to Harry's wizardry. Ron, on the other hand, might be a bit more cautious at first. He'd probably make some jokes about Harry being part ice - prince or something. Dumbledore would be very intrigued. He'd see Harry's new powers as an asset in the fight against evil. He might even offer to help Harry explore and control his ice powers better.
Harry might be in awe of Elsa's powers at first. He would likely approach her with caution and respect, as he does with most powerful beings. Elsa, on the other hand, would be curious about Harry's world of wands and spells. They could start by sharing their stories. Harry would talk about Voldemort and his battles, and Elsa would share her experiences with her frozen kingdom and her isolation.
Hermione could be quite popular. In the fanfictions, she might be the one who tries to figure out the science or magic behind Elsa's powers. Another could be Ron, who might be initially skeptical of Elsa but then grows to be her friend. Olaf from Elsa's world could also be popular as he brings his unique brand of humor to the mix when he enters the wizarding world.
Probably Harry Potter and Indiana Jones themselves. Harry's knowledge of magic and his experience in fighting dark forces could complement Indiana Jones' skills in exploration and combat outside of the magical realm.
Hagrid, of course. He loves all kinds of strange and dangerous creatures. He would be the first to be intrigued by the Indominus Rex and would probably try to approach it to see if he could take care of it or at least understand it better.
Dumbledore could be another character. He is extremely powerful and wise. He might have some prior knowledge or intuition about Alduin's existence. He could interact with Alduin in a more diplomatic way, trying to understand Alduin's motives and perhaps find a way to co - exist peacefully if possible. Or, if Alduin proves to be a threat, Dumbledore would be one of the few who could stand up to him.
I think Ron Weasley would be one of the characters likely to interact. He's always up for an adventure, and the wildness of Neverland would appeal to him. Ginny Weasley could also be involved. She's brave and strong - willed. From Peter Pan's side, Tinker Bell might interact with the Hogwarts students. She's feisty and would be curious about these new arrivals with different kinds of magic. And of course, the Lost Boys would be eager to meet the wizards and witches from Hogwarts.
Definitely Harry Potter and Optimus Prime. Harry is the hero in the wizarding world, and Optimus is the leader of the Autobots. They both have a strong sense of justice and would likely team up to face big threats. Another pair could be Hermione and Bumblebee. Hermione's intelligence could be used to understand the Transformers' technology, and Bumblebee's friendly nature would make them get along well.