So a lot of people suspect that Chat Noir is going to turn to the dark side in season 3; most likely because he finds out Hawk Moth is his dad and that he’s trying to save Adrien’s mom.
The most proof for this theory is the intro picture here:

Where Ladybug and Chat Noir are on opposite sides, with Chat being closest to the villains.
While this picture could indicate Chat becoming an antagonist, I always thought Ladybug and Chat being on opposite sides was because they are the main character and it was in order to make the rainbow effect work.
Something other that points to the “Chat becomes an antagonist” theory is this recent teaser pic for season 3:

which you might note is lacking Chat.
I heard that the pic was debunked as fake though, but that might not be true in and of itself.
Something else I wanna talk about is Le Paon:

We know that she’s going to arrive; probably in the Season 2 finale or first episode of Season 3.
There has been a lot of discussion about who she is, most people thinking she’s Emilie, Adrien’s mom, since it seems like the Peacock Miraculous belonged to her.
While I have before expressed scepticism of this theory because of Le Paon and Emilie’s different facial traits, this speculation is based on if this theory is true.
First of all, why is Le Paon’s skin blue? We haven’t seen any Miraculous holders’ skin change color in the show (although previous Ladybug Holder Mudekudeku’s skin changed color when transforming, but that was because her skin change was based on otjize paste, and since the miraculous holder’s transformed look is now confirmed to be based on the holder, unless the skin color change holds some significance to the holder, Le Paon’s skin color is still an anomaly.)
I was then reminded of something Nooroo told Gabriel in the Origins episode; “bad things happen when you use miraculouses for evil”. I don’t think those were Nooroo’s exact words, but that was the gist of it, and I think this is the reason for Le Paon’s skin change and what might have happened to Emilie.
If you will bear with me for a moment, take a look at this character:

People who know about Overwatch will recognize her, but to the people who don’t, this is Widowmaker. She was previously a ballet dancer, married to a highranking official in a global taskforce. She was kidnapped and brainwashed by a company called Talon to murder her husband. Afterwards, they furthered the brainwashed and even artifically lowered her body temperature to the point where she can’t feel any emotions aside from when she kills people.
Her real name is
Amélie.
Now this is probably all coincidential, but it does illustrate what I think happens to a person if they use miraculouses for evil; they become basically dead inside, to the point that even their skin change color due to a lowered body temperature, and they feel nothing except for when they commit acts of evil.
I don’t think Emilie stole the book or the Butterfly and Peacock miraculous, mostly because Master Fu was a young boy when that happened. And I don’t think she even started out using the Peacock miraculous for evil. I think she started out trying to be a hero but slowly fell into villainy. (I also think she didn’t do any of it in Paris, because I feel like the citizens would have mentioned her by now. Maybe she did it in the cities she visited during filming her movies, but wanted to focus on spending time with her family while home.)
Gabriel realized that something was wrong and confronted Emilie about it. Emilie having been taken over by whatever corruption occurs when miraculous are used for evil, offers her husband and the Butterfly miraculous, maybe even offering that they take over the world together.
I think the room we saw in Gorizilla was Emilie’s lair, just like how Hawkmoth has a lair, and I think when Emilie showed it to Gabriel, he panicked, took her miraculous (or maybe she never wore it when home and the vault behind her painting was originally hers) and locked her in there.
His wife was declared missing, and Gabriel searched desperately for a way to save his wife. When nothing seemed to work, he decided in a last ditch attempt to use one of the miraculous, but he chose the Butterfly instead of the Peacock, either out of respect for his wife or fear that whatever had done that to her was tied to the Miraculous itself.
Therein comes his conversation with Nooroo in the Origins episode, where he learns that the Ladybug and Black Cat miraculous can fulfill any wish when brought together.
If all of this is true, I think Emilie is going to break free in Season 3 or the Season 2 finale. Gabriel and Adrien will learn about each other’s miraculous, and Adrien will decide to help his father heal his mother.
I remember that there was a leaked image showing Ladybug and (it was either) Hawkmoth or Gabriel in the lair under Adrien’s house, the one I think holds Emilie. Maybe Ladybug also learns what Hawkmoth wants to use the Miraculous for (without learning that Chat Noir is Adrien), but refuses to let Hawkmoth have hers since in order to cure Emilie’s corruption, someone else would be afflicted by it.
This would lead to a Season 3 where Chat Noir and Ladybug work on opposite sides. Chat feeling that Ladybug has betrayed him by not helping him save his mother, and Ladybug trying desperately to reach Chat and convince him that using the Miraculous to heal his mother is a bad idea.