Red survived his injuries thanks to magic inherited by his ancestor, ThadeousIn the world of movies, it's perfectly normal for a person to be spitting image of their ancestor. It's plausible that Red's ancestor is Thadeous, and that it is thank to one of Thadeous's magical adventures that Red was able to survive two gunshots, and explosion, a broken neck and countless head injuries. Perhaps Thadeous wound up drinking some magical potion that gave him and his descendants magical healing abilities; or maybe Isabel had some non-human blood in her (would you put it past that inhumanly badass warrior woman to be part elf, nymph or goddess?); or maybe it was someone else down the family line. But in short, it is Red's ancestral connection to the magical land of Mourne that allowed him to survive so many injuries that would kill a mortal human.
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