1. Callback To The Karate Kid Cartoon
You might be thinking, "Wow, Cobra Kai made references to all three films!" (I know there's a fourth film, The Next Karate Kid, but we don't talk about that.) However, the show also included a nod to the animated series of The Karate Kid. The cartoon focused on Daniel and Mr. Miyagi travelling the globe to look for a sacred shrine with mystical powers. Although this shrine does appear in the Miyagi-do dojo, there's a much bigger Easter egg in Season 3.
In the last episode, we learn Kreese was a prisoner of war during Vietnam and was forced to fight other prisoners to the death on a log over a cobra pit. As hard as it is to believe, this idea was taken directly from the cartoon. In the pilot episode, Daniel is forced to fight a tribal chieftain on a log over a pool of lava.
Because the animated show is so silly (and downright terrible), you would never expect Cobra Kai to make a major reference to it. Ironically, it found a way to incorporate the cartoon and make it incremental to Kreese's backstory.