I picture the trailer for Mona be animated by Ko Takeuchi, and would go something like this:
Mona is just working at the gelateria from the first game, with Joe at her side. 9-Volt shows up and orders the usual thing he orders, probably something like triple fudge cookie dough with lots of sprinkles.
It's a slow work day so 9-Volt chats with Joe and Mona about how their day is going, and Mona brings up that she almost didn't arrive to work on time because she had stopped to read a letter someone sent her. She thinks it was inviting her to some sort of party, but her schedule is all booked up for the next month, so she decided to toss it away. Shame too, because it looked all fancy, and the envelope even had some kinda red wax seal on it.
9-Volt, at first, just keeps playing his Switch. But after a moment he stops and pauses the game.
"Wait... did you say a red wax seal?"
Mona replies "yeah, what of it?"
"C... can I see this letter?"
"Sure! It's right over there in the bin."
9-Volt digs the letter out of the trash, reads it for a moment and starts quivering.
"M... M... Mona! Do you have any idea what this letter is?!?"
After some explaining, Mona comes to realize that this invitation is to something considered among video game characters to be a very prestigious event, and it's one of the things Wario keeps being invited to. She sighs, knowing she has no time to do something like that, but Joe is aware that an opportunity like this doesn't come very often, and so he tells Mona she can take a paid vacation. Mona's eyes suddenly alight, and she asks Joe if he means it. Joe says he can hold down the fort while she's away and that this counts as an occasion that's too special to pass up, especially considering how hard and diligently Mona's been working for him over the past several years. Mona picks up the crumpled letter and thinks for a moment. Smash cut to Mona riding down the highway, several different angles of her scooter covered in travel stickers and with her bags packed, pan to her front side, freeze frame,
"Mona hits the road!"
Gameplay footage follows.