I just had a dream where I was watching Book 4 of the series and out of nowhere it ended up with Korra being poisoned to death which shocked everyone besides the other characters. This also wasn't the final season as there was a Book 5 which showed a baby being born thus implying the new Avatar and confirming the previous one's death. While most of the book focused on the characters cooping without their friend, the new Avatar was put through the items test by the White Lotus Society and soon training with his earthbending.
This new Avatar is just as headstrong as Korra was leading to some interesting confrontations with the other characters, especially Tenzin who was probably devastated the most by the news of Korra's passing. Jinora doesn't believe the news so she does her spirit body trick to go see for herself. Suyin who was present with the other characters for whatever reason said she was currently in the infirmary of Zaofu. Then something weird happened, Jinora's spirit body was unable to pass through the walls of the building which lead her to come back only to hear Suyin say something about how the type of metal used for the walls of the city buildings were so strong that it can keep out spiritual energy. I think they even said it was a layer of platinum, lead, and silver for whatever reason leading to me questioning why the hell silver is always used for supernatural elements. Suyin tells Jinora to go through the flooring as it was constructed using very basic metal.
Next we see Jinora trying to get through to the infirmary by sinking into the ground trying to get passed the thick walls buried beneath until finally she was able to make it through only to see Avatar Korra laying their in bed motionless without her stomach expanding and disbanding. It was then Jinora knew the news were true. She took a moment to kneel beside her friend as she started to cry as she reached her hands out to Korra's before she returned to her body.
I presumed this was the work of Zaheer and his cronies. Upon hearing the news of Korra's death, Bolin was heard celebrating from the other room as if he was glad that she died and he was just letting off frustrations. It was very weird yet he later become more sadden by her untimely death. Since this was a new season, all of this happened in Book 5 and the dream even extended into a Book 6 (the latter half of season three). Book 6 was merely nothing but the characters trying to get used to the fact that there was a new Avatar and the new Avatar getting frustrated that everyone compared him to Korra when he was his own person. Bolin offered to be his new earthbending bro. Tenzin offered his support and promised to be the new Avatar's airbending instructor. Jinora agreed to help him get in touch with the spiritual aspect of being the Avatar. And only a glimpse of what appeared to be a ghost Korra much in the similar fashion of Avatar Roku communicating with Aang. The dream and season ended before I saw the new Avatar become a fully realized one.