how would you do a Jackie chan adventures crossover with Miraculous?
Sorry it took me so long to answer. I really needed to think about this one. Thank you for the ask. And happy New Year.
Honestly, if I had to do this crossover specifically, I'd likely go down two paths with everything we have for Miraculous now and all the J.C.A. elements. Either Gabriel finds Shendu's statue first, along with his Miraculous, and uses his akumas to find the talismans for Shendu, or Valmont is part of The Kingdom.
With either option, it's a good way to mix the plot because Valmont could call Gabriel for some extra help collecting the talismans using his Akumas if he were part of The Kingdom. Meanwhile, Gabriel could have Tohru and the Enforcers as Adrien's bodyguard team if he replaced Valmont. Though I think Valmont, as part of The Kingdom, is more interesting.
Plus, if both are defeated, you could do more with The Kingdom by having them end up being the ones to help future J.C.A. villains achieve their own ends. Like, having Tomoe work with Tarakudo. Or Nathalie works with Shendu to free the Demon Sorcerers if they agree to help free Gabriel.
Aside from the villains, I'd also likely have Marinette be Jackie's niece, like Jade. And the plot with Hawkmoth and Valmont would be in the same city due to their connection. So, either Paris or San Francisco.
Because of that, I like to picture Marinette getting dragged into joining Jackie's adventures because of Jade, and that's how Ladybug always shows up on the scene, even if they're somewhere like Mexico when they met El Toro. Meanwhile, Cat Noir always appears due to Gabriel and Nathalie choosing to bring him when they have a new lead on a talisman.
And that's probably how I'd structure the overall crossover.