help needed making a foil for Fanfiction

[Benny 3]

So I've started a new fanfiction, and I have a brilliant idea for how I want to develop my characters.

 

So the story goes like this:

 

Queen Chrysalis crashes and barely (as barely as barely gets) survives after "A Canterlot Wedding". She gets back to her castle and sends what few remaining changelings she has to capture Fluttershy and convince her to feed Chrysalis her love. Fluttershy reluctantly agrees. She meets a regular changeling named Dirge, who is a foil so he's more bold and disobedient (but he still loves his queen like everyone else).

Throughout the fanfic, Fluttershy slowly loses her compassion and even helped invade Cloudsdale when she saw ponies she didn't like. (maybe the bullies who picked on her) Eventually, Chrysalis sends Fluttershy and Dirge to capture Twilight, so she may have her revenge. (note: Chrysalis never fully recovered, and has been slowly dying)

When Twilight is brought to Chrysalis, the queen shows her the queen transformation room, where a large cocoon lies dormant. Chrysalis says this will be her revenge, making Twilight the new queen of the changelings. Fluttershy, however, gets really upset about that and steals into the cocoon herself. She anted to be the new queen, she deserved to be queen.

Chrysalis tries to stop her, but dies in the process. Twilight leaves and Dirge cries over his queen. Fluttershy reemerges as an all-powerful version of a changeling: an Anti-Changeling. Her hatred had become her food, instead of love, and she wants to make everyone hate her at all costs. Dirge becomes her submissive slave who does her dirty work.

 

Basically, the only thing I wanted help with is how to go about making Dirge a memorable foil, and also pulling off this foil role reversal at the end? (or actually more like halfway point)

What can I do to make Dirge an opposite, but also a partner, to Fluttershy?

 

If you need me to explain more, just ask me. I'm pretty bad at explaining things.