Kai should not have been in KFP 4 since his soul was obliterated by Po in the Spirit World.

Shen being in KFP 4 could have worked if they actually did anything with him.

I liked seeing Kai again, but he should be deader than dead. It doesn't make sense how he can still be around.

Yeah!

Shen's return made sense. Kai's return did not.

But it was great to see them nonetheless. It would have been greater for them to have dialogues.

There are several theories that we can make out as an excuse. Kai was not obliterated, he might have been just deprived of his chi powers and sent to another part of the spirit realm. Chameleon reassembled his essence while summing him with the Staff.

After watching the film, I kind of wished that only Tai Lung was brought back instead of the Kai or Shen. Plus, I kind of wished that they characterized the Chameleon more since we don’t know much about her past besides being a power hungry sorceress (there are also a lack of flashbacks revolving around her past, unlike the other three KP big bads).

There are a lot of reasons why she did not get a flashback

Firstly the movie was supposed to be a live action and animation hybrid with Chameleon being a human sorceress called the Collector. Gladly this was scrapped away.

Then Mike Mitchell did not want any backstory for Chameleon or any flashbacks for Zhen. It was after several persuasions from the writers that he agreed to animate flashbacks for Zhen but there was no time to animate that of Chameleon so they gave her a one line backstory which I think was pretty valid.

I see it now. Also off topic, I don’t think she would be heinous enough to pass the Heinous Standards since her “take over the world” plot relies on fridge horror.