So you all know the PPG reboot and the infamous panda Allegro. I don't like him either, as he's an annoying and one-dimensional creep.
However, I seriously cried when I learned about Largo, as it reminded me of my life... As you can see, Largo is from the Cosmic Bear (His sadness while Allegro is his happiness). While I don't like Allegro (Too annoying and one-dimensional), Largo is... Rather sympathetic. I just feel for him, as someone who has suffered from depression before (Both of my grandmas died in 2016, and I suffered from depression in the next year due to my shitty vacations and my shitty 15th birthday. I felt like a fucking GUEST in my OWN house.) You're empty, and feel that nothing will make you better.
So, here's my idea (A long, special episode, like The Powerpuff Girls Rule!!!), called Furies of Sadness (Inspired by Touhou 15: Legacy of Lunatic Kindgom). The whole city is depressed (Even the villains), with the only one who isn't affected being Bubbles, as she is very happy and optimistic (After Blossom, Buttercup and Professor Utonium had a frustrated day, they were affected as well). With the whole world being taken over by sadness, pessimism and depression, Bubbles decides to find out where it all comes from while defeating and knowing new villains. The antagonist is Largo, a depressed spirit bear, wanting revenge on humanity after Allegro (His brother) killed his wife and children (Implied, since it's a kid's show, with Largo saying "My brother eliminated my family"). After Bubbles defeats him in a big battle, Largo teams up with her to kill Allegro, and they do after another big battle. And so, Bubbles saves the world.