The characters' interactions would be really interesting. For instance, Ford from Gravity Falls, being a scientist, would be fascinated by the magic in Equestria. He might try to find a scientific explanation for it. Fluttershy would be a bit shy around the Gravity Falls humans at first, but would soon open up. The ponies' positive and friendly nature might have an impact on the more cynical characters in Gravity Falls, like Soos. He could learn a lot from their friendship values. Meanwhile, the Gravity Falls gang could introduce the ponies to new things like s'mores and camping.
Well, I think Lance would be really intrigued by Mabel. He'd probably be impressed by her colorful sweaters and her positive attitude. Mabel, on the other hand, would be excited to meet a real - life space hero like Lance. She might even try to set him up with one of her friends in Gravity Falls.
Mabel and Hilda would be fast friends. They both have a love for the strange and wonderful. Mabel would be excited to show Hilda her sweaters and all the cool stuff in the Mystery Shack. Hilda would share her adventures in Trollberg with Mabel. They might even come up with some new and crazy ideas for adventures together, like having a slumber party in a haunted forest. Wendy would probably be a bit more aloof at first, but as she gets to know Hilda, she'd start to warm up and they could go on some more adventurous outings, like climbing a really tall mountain in Hilda's world.
Bill Cipher would be a major wildcard in their interactions. If he were to cross paths with the Winchesters, he would likely try to manipulate them for his own amusement. He might offer them false information or try to pit them against the other characters in Gravity Falls. The Winchesters, being used to dealing with devious creatures, would have to be on their guard and figure out a way to outwit Bill while also trying to solve whatever mystery has brought them to Gravity Falls in the first place.
One idea could be that Dipper and Mabel end up in Equestria. Dipper might be intrigued by the magic there and start studying it, while Mabel could make friends with the ponies easily. Maybe they help the ponies solve a mystery that's been plaguing Equestria, like strange disappearances. Another idea is that a pony from Equestria somehow travels to Gravity Falls. It could be Twilight Sparkle, who is amazed by the different kind of 'weirdness' in Gravity Falls compared to Equestria.
Mabel would be excited to meet the Winchester brothers. She might try to get Dean to tell her all his hunting stories and would probably try to knit them some cool accessories. She could also introduce Sam and Dean to Waddles. Dipper would be a bit more cautious around them at first, but as they started working together, he would respect their skills and knowledge. The characters would need to learn to trust each other quickly since they come from different worlds but are facing similar threats.
In a crossover fanfiction, the interactions would be really interesting. Ford, if he were involved, would be very intrigued by the animatronics. He might study them to see if they are related to any of the other interdimensional beings he has encountered. Dipper would be the voice of reason, warning everyone about the potential danger. Mabel would try to find the good in the animatronics, perhaps believing that they are just misunderstood. Soos would be the comic relief, making jokes about the animatronics' appearance. Wendy would be the tough one, ready to fight if necessary. The animatronics themselves might be confused by the Gravity Falls gang. The ones that are more aggressive might see them as a threat, while the more docile ones might be curious about these new visitors.
Another theme is the use of magic and the supernatural. My Little Pony has a lot of magic, and Gravity Falls has its own share of supernatural elements like the Journal and various monsters. Fanfictions may combine these aspects, like a story where the magic from Equestria interacts with the strange phenomena in Gravity Falls. This can lead to all sorts of interesting plot developments, such as the ponies using their magic to help fight off the creatures in Gravity Falls or vice versa.
Many of these fanfictions also explore new themes that neither of the original shows might have delved into deeply. For instance, how the Gravity Falls anomalies might affect the pony world in ways that are not just about solving a mystery, but also about changing the relationships between ponies. It can be about the ponies learning to deal with a more 'human' or 'weird' kind of situation, which is a fresh take on both universes.
Pinkie Pie would be all over the Pokemon, throwing parties for them and making new friends easily. The more energetic Pokemon like Charmander or Cyndaquil would probably be drawn to her fun - loving nature. She would introduce them to all the fun things in Equestria like parties and games.
Well, the ponies and Ice Age characters would interact based on their different strengths and personalities. The ponies, with their magic and unique abilities, could offer new solutions to the problems the Ice Age characters face. For example, Twilight Sparkle could use her magic to create warmth in the cold Ice Age environment. In return, the Ice Age characters could teach the ponies about survival in a tough, natural world. Manny's strength and leadership could inspire the ponies, and the ponies' sense of community and friendship could have a positive impact on the relationships between the Ice Age animals. They would likely have to overcome some initial misunderstandings due to their very different worlds and cultures, but in the end, form a strong bond through their shared adventures.