Here's what it came up with. (Also, I told it Sokka and Katara's last names are Clearwater as they don't have actual last names, and someone in 2016 said that would be a good last name.)
1. Avatar Aang used to be a spy but didn't realise as he has been suffering from amnesia.
2. Katara Clearwater poisoned Avatar Aang at the beginning of the story, and it's taken the whole story to take effect.
3. Katara Clearwater is actually Avatar Aang's daughter.
4. The whole plot is a premonition, not reality.
5. Katara Clearwater wasn't born but created in a lab.
6. Katara Clearwater is just a brain in a jar.
7. The goodies and the baddies all actually want the same outcome and have to work together in the end.
8. It's really ten years into the future.
9. Sokka Clearwater has been possessed the whole time.
10. Avatar Aang turns to the dark side.
11. Sokka Clearwater is really a vampire.
12. It turns out they are all living in a computer game.
13. Sokka Clearwater's delirious ramblings are actually a premonition
14. Sokka Clearwater was switched with another baby at birth.
15. The entire story is a figment of Avatar Aang's imagination. He wants to prove what a great story teller he is.
16. Avatar Aang has secret powers resulting from a strange potion.
17. Sokka Clearwater is actually Avatar Aang's son.
18. The entire plot was a ruse designed to teach Katara Clearwater a lesson.
19. Katara Clearwater was just using Avatar Aang for money.
20. Sokka Clearwater faked his own disappearance.
21. During the course of the story, Avatar Aang picked up the secret to eternal life and therefore doesn't die.
22. The narrator is unreliable and half the plot never happened.
23. Katara Clearwater has been dead all along.
24. The story is just one iteration of an infinite loop.
25. Sokka Clearwater has been an action figure all along.
26. The whole plot is a film, rather than reality.
27. Avatar Aang's dream was not a premonition and meant nothing.
28. It turns out they are all horses.
29. Earth has been destroyed and they're all living in a virtual reality.
30. The town they live in doesn't really exist.