Guy and Hiccup's relationship could go either way. On one hand, Guy's ingenuity and Hiccup's brains would bring them closer. They would be constantly working on new things and inventing stuff. On the other hand, their strikingly similar personalities would completely clash. They would often bicker or argue about who's invention is better. Also, his pet sloth, Belt, would make quite good friends with Toothless, due to their comical and dramatic personalities. Guy plays a major role in Dreamdorks alongside Jack and Hiccup.
Jack and Guy would be best friends, almost brothers. They have a lot in common, both being from the past. Also, they are clever and trouble-making. Guy would most likely end up trying his inventions out with Jack (who wouldn't have a problem with it either). This would bring them even closer together. Guy also has a big part in Dreamdorks, with Hiccup and Jack. They also have a pairing called, Guyfrost.
Merida and Guy are very much alike. Strong and good-hearted, these two would find each other very interesting. They have trouble fitting in, which is something that they could bond over. They have a romantic pairing, called Meriguy.
Guy and Rapunzel would be good friends. They are both nice, caring people (also very smart). As with Hiccup, Belt and Rapunzel's pet chameleon, Pascal, would get along quite nicely.
Since Grug - and by extension the rest of the Croods - are ruled by fear, Pitch would possess great disdain towards Guy. While it is never really stated outright, it is possible that Pitch was around back in mankind's infancy, teaching mankind to fear the dark for their own safety, so it is possible that Pitch held some influence over the Croods. Because Guy helps the Croods move beyond this, this could mark the moment when Pitch was losing his power and would become mankind's adversary.
Friends and AlliesEdit
Guy and Elsa would be good friends (if not, more). Elsa would be greatly interested in Guy's "inventions" as would Anna. Their ship is Guyelsa or Gelsa.
Anna would also be amazed at Guy's creations. She would try to use Guy's stuff, and in the process, accidentally break it/them. They are both strong-willed and awkward-ish, so they would be highly compatible. Their ship is Guyanna or Ganna.
Hiro would be one of Guy's best friends. Guy would most likely be very enthralled by Hiro's technological prowess, sparking a strong friendship. Guy would be the type of friend that would stand by Hiro when he lost his brother.
Guy and Oncie would have a relationship similar to that of Guy and Hiccup's. They could butt heads, having disagreements regarding inventions, or using the inventions as the glue that holds them together.
Guy would feel uneasy around Ralph. Ralph's size and demeanor would remind Guy of Grug, and the tension between them. But, like with Grug, they would eventually become good friends and overcome the tension.
Guy and Vanellope would have great amounts of fun together. Guy would spend large amounts of time "tricking out" Vanellope's cart, and they would practice on the race track.
Guy would automatically become suspicious of Hans, because of his oddly charming personality and sly attitude. Because of his likely friendship with Anna, he would know about him and dislike him.
Guy would hate King Candy. Since Guy would be friends with Vanellope, they would be rivals on the race track. Since Guy would be helping Vanellope, he would not trust or like King Candy.
Before the Croods came along, Belt was Guy's only companion, so their relationship together is strong. They will both interact, and Guy will even talk to and understand Belt at times. Belt loves to help Guy with things and emphasizing certain moments, like adding a "Dun dun daaa!" to intense moments or if something bad is about to happen.
Guy is Eep's love interest. They met on a cliffside, where Guy showed Eep fire. Eep was immediately interested in the fire and wanted to be friends. While the "end of the world" was underway, Guy went with Eep's family to a higher area. He eventually bonded with the Croods and became Eep's boyfriends, much to the dismay of her father, Grug.