When I first saw the flashback in the episode of Highlander in which Duncan is banished from his family and village for being a "changeling", I didn't think much about it. Okay, the concept of a fairy changeling fits in with the Celtic culture of the Highlands. Later, I realized that — Highlander Immortals ARE changelings, specifically human-fae hybrids! It explains so much. Most cultures in the world have myths and legends about immortal, supernatural beings analogous to elves and fairies, so this theory works everywhere, not just in Britain and Europe. All Highlander Immortals whom we're aware of are orphans whose parents are unknown. Because the fae don't want halfbreeds among them, they foist these babies onto human families as changelings. Because they don't want too many of the halfbreeds around to cause trouble, they invented and promulgated the Game with that ridiculous "There Can Be Only One" premise, to get the halfbreeds to kill each other off. And of course the fairy genes account for their longevity and the difficulty of killing them. Can't have children? Most interspecies hybrids are sterile.
According to the series, they're all foundlings as well.
In the first movie, Connor does in fact follow Ramirez's advice on how to fight the Kurgan: he uses heart (Brenda saves his life), soul (by demonstrating courage and skill and care for others) and steel (he decapitates the Kurgan with Ramirez's 2500 year old sword). Made a great movie even better!
In the season 1 finale, "The Hunters," Horton attacks Duncan with a taser in an attempt to immobilize him. But Duncan managed to fight through the voltage and pull the prongs out. The first time I saw this episode, I thought there would be no way he could do that, regardless of how tough he was, because tasers inhibit motor functions. He wouldn't have been able to move. A few years later, I read about the history of the development of taser technology. Around the time this episode was released (1993, I think) the high-powered tasers that inhibited motor function didn't exist yet (those didn't come out until 1998). It was actually very common for people on PCP, or with just a high tolerance for pain, to be able to fight off the older tasers because they were only designed to shock the attacker into submission... which is why the ones we have now use an electrical charge that's the same as the electrical signal the brain sends down to the body, shorting out all muscle control. Basically, if Horton had used one of the modern tasers, the show wouldn't have lasted more than one season.
In the first episode Connor tells Duncan someone should keep an eye on Richie when he witnessesa duel(Duncan agrees and it's how he ends up taking him in). When watching the show the first time it comes of as because he knows about immortals, but the meaning changes when watching it again after the second season episode where Richie becomes immortal. Duncan and Connor both knew Richie was pre-immortal and that's why Duncan took him in, so he could there to teach him if his immortality was awakened.