So... Here we go. It is important that you are playing Scarlet as a female with the standard autumn uniform for the theme...
Lycanrock (Dusk) (male)
Dauchsbun(male)
Maschiff (male, preferably shiny, give it everyone, as evolved it doesn't fit the theme)
Mudsdale (male, bit of a stretch, but shiny is preferred here as well. Flying for a Tera type ... I mean he should have some balloons in his birthday)
Banette (for the doll, I guess) or you can go with an axew, to pay homage to duckie, which is also why Scarlet is important+other than outfit coloration)
Can you guess the theme?