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 vampires in Twilight are often more reserved and struggle with their inner 'humanity' more than those in True Blood. So, a character like Carlisle from Twilight might try to teach some of the True Blood vampires about self - control. In return, a True Blood vampire like Eric could show Carlisle how to be more assertive in the vampire world.
The Flash's super - speed can be really useful in the Supernatural universe. He could quickly move between locations while hunting monsters or escaping dangerous situations. For example, if Sam and Dean are surrounded by demons, the Flash could use his speed to rescue them. On the other hand, the Winchesters' knowledge of the supernatural can help the Flash deal with threats that have a magical or otherworldly origin in his own city.
The wizards would likely be cautious at first when interacting with True Blood vampires. They might see them as dangerous and unpredictable. For instance, Harry Potter himself would probably keep his wand at the ready. The vampires, on the other hand, might be curious about the wizards' magic.
Naruto's chakra - based abilities like Rasengan could interact interestingly with Wakfu magic. Maybe the Rasengan could be enhanced by infusing it with certain Wakfu elements. On the other hand, Wakfu spells might be disrupted by Naruto's strong chakra flow. For example, a spellcaster in Wakfu might find it difficult to cast a spell when Naruto is nearby releasing a large amount of chakra.
Naruto's ability to create multiple clones could be really useful in Inuyasha's world. He could send clones to scout for demons or to distract them while Inuyasha attacks. Inuyasha's Tessaiga, which can cut through almost anything, could be used to break through some of the tough defenses that Naruto's enemies might have. For example, if they faced a really strong earth - style jutsu - created barrier, Inuyasha could slice through it.
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.
The fire - based abilities of Natsu from Fairy Tail and the ice - based abilities of Hitsugaya from Bleach could create some really cool interactions. Natsu's heat might be able to counteract Hitsugaya's ice in an interesting way, like when they fight together against a powerful foe. Their different combat styles, with Natsu's more brute - force approach and Hitsugaya's more calculated and precise strikes, could also make for an exciting combination.
Naruto's chakra - based abilities, like the Rasengan, would be a huge shock to the Vampire Knight characters. They have never seen such concentrated energy attacks. Meanwhile, the vampires' superhuman strength and speed could be a challenge for Naruto at first. But he could use his shadow clone jutsu to outnumber them. For example, if a vampire tries to attack him with speed, he can send out clones to surround and counter - attack.