Gathered up some content from the writers' commentary on "Evolution".
Soooo, they apparently considered in a fit of madness to make the entirety of season 5 happen all on the same "day".
They also were brainstorming impossible names for all the Monarch power fusions.
The moment where Rabbit Noir and Monarch were fighting, falling from the top of the Eiffel Tower (with past-Ladybug and Cat Noir also falling but not noticing them), was from "Bubbler".
One day, we'll see the whole Animan "falling in love" scene between Alya and Nino animated.
Ladybug and Rabbit Noir apparently wounded up some time back in 1939-1940.
Marianne (Master Fu's lover) was based on Frédéric/que Engel Lenoir's great-grandmother (their mother's grandma), who was a militant during WWII.
Master Fu didn't really trust Ladybug upon seeing her come from the future, but her saying the same words as he does upon showing her the Miraculouses in spite of the great risk it meant convinced him that as it is something he would say, he can trust her.
Alix leaving to become Bunnix makes the writers cry every time.
They spent 4 hours deciding on the Lucky Charm before realizing they could just reuse the Heroes' Day mini-Miracle Box.
The moment where Monarch decides to follow Ladybug and Rabbit Noir back to that day solidifies when Gabriel finally goes over to pure insanity, abandoning the option of a second chance at life and instead pursuing his dark side and obsession.
In Ladybug's eyes, she and Cat Noir had a very special bond while back in season 4, he felt like he was "demoted" and just one member of the team left in the background.
The "heart" of the show is the "superpower of the heart", and that includes its ability to mess everything up (for Ladybug for example).
The argument between Nathalie and Gabriel was essentially a "separation", a breakup of sorts over whatever they've had previous seasons.
Lila overheard the argument between them (though how much isn't said) and is acting innocent in front of Nathalie.
The end of episodes endcards are named "Post Poster Paints".