DoubleO7

Kris & Susie end up on the set of My Friendly Neighborhood by accident (they're on a school trip or something & "accidentally" split off from their tour group).

They find out abt the fact that the puppets there are just alive somehow & decide to hunt down the method used to make them so that they can bring Ralsei & the other darkeners into the Light World Frankenstein style.

Options for what happens next:

It goes horribly wrong & they accidentally make a new puppet

It goes horribly right and Ralsei is there but Wrong somehow (maybe they were just really bad at sewing?)

Everything goes fine but now they need to figure out how to integrate puppet-ralsei into society.

They do not succeed in finding out the secret, but make friends with the neighbors along the way :)

They succeed but grabbed the wrong object to sew in so now they've got a darkener that is NOT ralsei running around.