Think about it. The Arrow team is all about using technology and their physical skills to fight crime in Star City. When they meet the Winchesters, who are used to dealing with ghosts, demons, and angels, there would be a huge culture shock. Oliver would initially be distrustful of the supernatural elements that the Winchesters bring. But as they face a common enemy, like a demon that is using high - tech gadgets to cause chaos in the city, they would start to work together. Sam would be trying to explain the supernatural aspects to Felicity, who would be fascinated and trying to find a scientific explanation for it all. And Dean would be teaching some of the Arrow team basic self - defense against supernatural threats.
Sam and Oliver would probably start off a bit cautious with each other. Sam, being the more cerebral of the Winchesters, would be interested in Oliver's methods of protecting the city. Oliver, on the other hand, might be a bit skeptical of Sam's supernatural knowledge at first. Dean would likely bond with Diggle over their combat skills. They'd probably exchange stories about their battles, and Dean might even show Diggle some of his unique ways of taking down enemies. Castiel, with his angelic powers, would be a mystery to the 'Arrow' characters. Felicity might be both intrigued and a bit scared of him, but she'd also be eager to understand how his powers work.
If Castiel were to be in this crossover, he would be very confused by the walkers at first. He's used to dealing with demons and angels, not undead creatures. But he would quickly adapt and use his angelic powers to protect the group. Rick from The Walking Dead would see Castiel as a valuable asset but also be a bit wary of his otherworldly nature. They would have to learn to trust each other as they both have the goal of protecting the survivors and finding a way to end the chaos in their respective worlds.
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.
Dean Winchester would likely be charmed by Lorelai Gilmore's sass and sense of humor. He might also be a bit protective of her, given his nature. Sam would probably have in - depth conversations with Rory about books and knowledge. Rory, in turn, would be fascinated by Sam's experiences with the supernatural. And Luke would probably be a bit suspicious of the Winchesters at first, thinking they're up to no good in his town.
The powers of the Supernatural characters, like Sam's psychic abilities and Dean's combat skills, would contrast with the more otherworldly powers of the Good Omens characters. Aziraphale's ability to perform miracles and Crowley's demonic powers would be on a different scale. For example, Sam's psychic visions might be able to predict events that Aziraphale and Crowley are involved in, but they might not fully understand how he gets these visions at first.
On the other hand, Sam and Dean's knowledge of the supernatural would be invaluable to Supergirl. They could teach her about different types of demons, how to detect them, and what weaknesses they have. Their skills in using various weapons like the Colt or salt - loaded shotguns could be combined with Supergirl's powers. For instance, Dean could shoot a salt - loaded shotgun at a group of demons while Supergirl uses her super breath to blow the salt towards a wider area, maximizing the effect.
Gibbs from NCIS would probably be very skeptical of the Supernatural elements at first. He's a man of facts and evidence. But as he sees things that can't be explained, he might start to open up. Dean Winchester, on the other hand, would likely be impatient with the slow - moving NCIS investigation process. They would need to find a middle ground to interact well.
Dean would probably be very suspicious of Hannibal from the start. He's seen a lot of bad guys, and Hannibal's calm and collected demeanor would set off his alarm bells. Sam, on the other hand, might be more interested in understanding Hannibal's motives. Hannibal would likely see the Winchesters as fascinating specimens. He might try to analyze their relationship and use it to his advantage.
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.
In terms of magic, the witches in 'True Blood' have their own brand of magic which is different from the magic and spells we see in 'Supernatural'. If they were to interact, there could be some unexpected results. Maybe a spell from a 'True Blood' witch could enhance the power of a weapon used by the Winchesters. Or a spell from 'Supernatural' could backfire when used in the world of 'True Blood' due to the different magical rules in each universe. This could lead to some comical or dangerous situations as the characters try to figure out how to work together.
The characters would interact in interesting ways. For example, Eleven could use her powers to help the Losers' Club against Pennywise. Mike from Stranger Things might befriend Bill from the Losers' Club quickly as they are both natural leaders. Dustin would probably be fascinated by the Losers' Club's knowledge of the town's mysteries and share his own scientific insights.