7. Mother Gothel Is The Evil Queen From Snow White
There's plenty of theories out there that link various Disney movies, but most are only superficial, merely putting them in the same world. This one directly links the plot of two movies released seven decades apart.
In Snow White The Evil Queen is obsessed with beauty, going to almost-murderous lengths to be the most beautiful in the kingdom. In Tangled Mother Gothel is obsessed with youth, kidnapping a girl and holding he captive for years just to retain her young looks. Aside from looking similar (they both have haggard alternate styles), there's a lot to link the two; they share motives and both have a penchant of daggers. Are they actually the same person?
Essentially Gothel's entire existence is built around retaining her youth, with Snow White and Rapunzel just representing ways to achieve that. This theory appears to fall apart when you realise both characters die at the end of their respective films, ruining any narrative cohesion, but given how much magic's at play it's entirely possible.