*Adrien's dad Gabriel is revealed as Hawk Moth (no surprise there). His ultimate goal is to capture the Miraculous and use their power to revive his comatose wife Emilie.
*Master Fu is revealed to be the last of an ancient order of guardians. He's training Marinette to succeed him in time, but it's teased that the order was destroyed by a mistake he made long ago.
*Ladybug and Chat Noir have obtained Kwami Food that temporarily upgrades their powers for rough terrain (underwater, arctic, etc.)
*Ladybug recruits Alya and Nino as part-time heroes Rena Rouge and Carapace, offering them Miraculous when needed and taking them back when done
*Chloe somehow manages to get a Miraculous by accident and becomes Queen Bee, but she's still Chloe and so the results are mixed at best. She at the very least cedes to Ladybug when she takes the Miraculous back
*In a fit of love-fueled desperation for her boss, Gabriel's assistant Nathalie has taken up the Peacock Miraculous to become Mayura and aid him in his campaign, but the Miraculous is damaged and is draining her life. It's implied that using it is how Emilie was put in her coma.
*After a full season of absence, Lila has made good on her return and is on the road to ruining Marinette as she slowly turns the whole school against her. She's become an ally to both Gabriel and Hawk Moth as he uses her to manipulate everybody as he sees fit
*Most recently, it's been revealed that a new Hawk Moth will rise in the future, and it will most likely be Lila.