The Goa'uld System Lords could also be very interesting. Imagine their reaction to an immortal Highlander. They would see him as either a threat or a potential source of power. Their attempts to either capture or eliminate the Highlander could create a lot of action and drama in the fanfiction.
Daniel Jackson from Stargate. He has a deep knowledge of ancient cultures and languages. In a crossover, he could study the origin of the Highlander's immortality, believing it to be related to some ancient alien civilization. His inquisitive nature would drive the story forward as he tries to understand the Highlander phenomenon.
Sam Carter and Methos would be a fascinating combination. Sam's scientific genius could be intrigued by Methos' ancient knowledge and long - lived existence. Methos might also be able to offer some unique perspectives on the technology Sam deals with in the Stargate program, and together they could come up with innovative solutions to problems.
Definitely Darth Vader and Jack O'Neill. Darth Vader with his imposing presence and dark side powers would be a formidable force against the Stargate team. Jack O'Neill, with his military experience and sense of humor, would be a great contrast. Their interactions could be really intense and full of conflict.
A common storyline is the clash of cultures. The military - oriented Stargate teams with their high - tech weapons and strategies meet the lone - wolf immortals of Highlander. There could be a situation where an immortal Highlander is mistaken for an enemy by the Stargate team. Or, the Stargate team might need the help of an immortal to defeat a powerful alien foe that is immune to their normal weapons. The immortals' ability to sense each other could also play an interesting role in a Stargate - Highlander crossover, like when they are on a planet full of hidden threats and the immortal's sense helps the team avoid danger.
Jack O'Neill from Stargate could be an interesting character to pair with Duncan MacLeod from Highlander. Jack's military experience and sense of humor would contrast well with Duncan's noble and sometimes brooding nature. Another good pair could be Daniel Jackson and Methos. Daniel's thirst for knowledge and Methos' ancient wisdom would make for great interactions.
Anthony Bridgerton would be a great character to include. His strong sense of family and his often stubborn nature could lead to some interesting clashes in a crossover. Say, in a crossover with a fairytale world like Cinderella. He might initially be against the idea of the Bridgerton family getting involved with the magic and 'foolishness' of the fairytale world, but then gradually change his mind.
One idea could be a Highlander character finding a Stargate and being transported to different planets. They could use their immortality to survive in the various dangerous situations on alien worlds and perhaps encounter Goa'uld who are interested in their immortality.
Definitely Harry Potter and Daniel Jackson. Harry has his own set of magical abilities and has faced many dark forces in his world. Daniel is a brilliant archaeologist and linguist in the Stargate universe. When paired together, they could exchange knowledge. Harry could teach Daniel about magic, and Daniel could introduce Harry to the ancient cultures and languages of the Stargate worlds. They could also work together to solve mysteries that require both magical and archaeological knowledge.
Darth Vader would be an amazing character to include. His imposing presence and incredible power would be a huge threat in the MCU. He could face off against Thor, with their different types of powers creating an epic battle. Another interesting character would be Kylo Ren. His conflicted nature could add an interesting dynamic, especially if he interacted with characters like Captain America who have strong moral compasses.
Definitely Nigel Marven from 'Prehistoric Park'. His knowledge and enthusiasm for prehistoric animals would make him a key figure in any crossover. If it was a crossover with 'Terra Nova', he could team up with the Shannon family. His expertise would help them better understand the prehistoric world they are living in and he could also learn from their experiences in a colony in a prehistoric environment.
The Prophet of Truth from Halo could also be an interesting addition. His devious plans and manipulative ways could create a lot of chaos in the Fallout universe as he tries to gain power over the different factions and their resources.