First off, let me just say that I for one cannot wait to see the reunion between Plagg and Tikki because it's been confirmed that the two of them know each other quite well. I wonder how they'll act around and\or towards each other? Soooooo excited!
Second, after the reveal, when Adrien and Mari hang out together, Plagg and Tikki will be able to interact with the other's Miraculous holder, right? So how do you think Mari and Plagg will get along? Or Adrien and Tikki? I personally think that it will be totally, hilariously adorable, especially if they sometimes end up with the other's holder! We have all witnessed how Marinette can resort to rash, somewhat irresponsible behavior from time to time, and that to me just screams Plagg.
''PLAGG! I accidentally sent Nino a text that was meant for Adrien! What do I DOOOOOOO?!''
''Pff. Steal his phone.''
We also know that Mari can be pretty sarcastic and quite a little jokester when she wants to be, so Plagg stirring up that side of her sometimes and the two of them just going at it about stuff together? Priceless!
And Adrien and Tikki? She would be so sweet about his life situation and just so caring and supportive when he gets upset or sad about his parents! She could encourage him to be the person underneath the mask he only thinks he can be when he's Cat Noir like she does with Mari, courageous, capable, confident. She can also reassure him that even as regular ole' Adrien he's just as special and invaluable as his alter ego. Then she'll cuddle his cheek like she does with Marinette and I will just turn into a pile of goo at the adorable grin that'll light up his precious face. It'll really benefit Adrien emotionally to have Tikki act as his loving and cuddly support system like she does for Mari, because I think we all know that ever since his mom disappeared, Adrien is both touch-starved and emotionally-starved. So to have Tikki be there to lend him a listening ear, or offer him encouraging words, or even just randomly fly up to him with this big smile on her face and nuzzle his cheek will probably be enough to make that kid's week. Because let's be honest, while we all love him, Plagg really stinks at being supportive, and stinks even worse at being cuddly.
But I'm getting off topic here. Back to business. Now I'm sure there will undoubtedly be times when Plagg might encourage Mari to do something she knows she shouldn't do and she'll stand firm about it, but come on, her breaking out into a mini speech about morality and justice and Plagg countering with a witty remark and then the two having a sarcastic argument would be so funny! Or Adrien might sometimes be about to do something stupid and Tikki'll pull out her 'now you know this isn't right' bit and Adrien will just hang his head and be like ''You're right Tikki, thanks for stopping me,'' and she'll just pat his head for being such a good boy.
Also, can we just talk about how Plagg'll probably very gladly enlighten Marinette about Adrien's 'hilarious' crush on her\Ladybug and get into side-splitting detail about the immensity of his pining?! I imagine Tikki'll most likely spill to Adrien about Mari's crush on him in a bit more of a dignity-preserving fashion, maybe even down-playing the awkward parts because let's face it, that boy is going to be dying for deets about his Lady's reciprocated affections! I also think the four of them getting into a kind of argument together would be pretty funny too! So basically I feel like we'll have Adrien and Tikki making a solemn oath to never leave Marinette and Plagg alone together, and Mari and Plagg vowing never to let Adrien and Tikki's lives get boring, and all four of them pledging to stay together and love each other forever and always.
And then you'll have me sobbing hysterically in a puddle on the floor because the feels are just too overwhelming.