When I was looking at Wind Archer's new costume, Night Raven of the Endless Void. I thought it was just going to be an updated look of his costume from Ovenbreak, Night Raven. But then I noticed the butterfly theme, and remembered that the Beast Cookies have bug forms that we are going to be seeing in the new story arc.

I believe the Beast Cookies corrupted the Guardians in this split timeline that Shadow Milk created. And I am skipping Eternal Sugar and Wind Archer because the costume already shares the butterfly motif.

Shadow Milk and Moonlight

• Both were created by higher beings, the Witches & Wizards respectively.
• The Original 13 Witches couldn't be with their creations, because they had been turned into Cookies by the Witch of Light to save their lives (unbeknownst to everyone), while the Wizards stayed with their creations until they left one day (Moonlight waits for the Wizards to return and she protects their city in the meantime).
• Shadow Milk is an expert in Magic, but he primarily uses Dark Moon Magic which "is most potent during the crescent phases." Moonlight is shown to sleep and ride on a Crescent Moon. And her Ovenbreak costume, Alluring Crescent Moon, is referred to as "darkMoon" in the game files.
• Alluring Crescent Moon deceives Cookies into following a scarlet path that "leads to a trap of eternal nightmares."
• Some quotes from Alluring Crescent Moon that sound deceitful.

>The moon has two faces.
Aw... bad dream? Tsk, too bad.
Have any nightmares recently?
How do you know you're really awake?
Follow the scarlet moonlight. You won't regret it... much.

Mystic Flour and Sea Fairy

• Sea Fairy's Ovenbreak costume, Dread Trident of the Abyss, is about Sea Fairy's failure to reach the night sky. And how she has confided herself to remain "in the abyssal depths for eternity... where the moonlight cannot reach."
• Sea Fairy basically falls to apathy. And Mystic Flour would encourage this.
• Some quotes from Dread Trident of the Abyss reinforce the feeling of apathy:

>All is void...
All is futile...
This was my destiny...
There is nothing to hold dear anymore...
In the end... the moon is forever out of reach...

Silent Salt and Millennial Tree

• Millennial Tree is the Millennial Tree. And Silent Salt created the Silver Tree with Elder Fairy.
• Millennial Tree's Ovenbreak costume, Primal Mercy, is about Millennial Tree selflessly giving up parts of himself to a self destructive level. "...it selflessly keeps giving, only ever wanting to fill everything with its brilliant mercy."
• Some quotes from Primal Mercy that sound like solidarity:

>I merely wish for peace upon these lands.
All living things are precious no matter their size.
Among all life there is no such thing as more important.
May these lands be forever prosperous...
May no cookie walk hungry.

Burning Spice and Fire Spirit

• Fire Spirit's Ovenbreak costume, Immortal Cataclysm, is about Fire Spirit engulfing the world in fire to turn it into ashes. Fire Spirit falls to his destructive impulses.
• Burning Spice is all about destruction and would approve.
• Some quotes from Immortal Cataclysm that scream destruction:

>I won't stop until the entire world is burning!
I won't stop until the world is a pile of ashes!
I won't stop until nothing but ashes remain!
Watch as the world BURNS!
We need to set it all blaze, and start from the very beginning.

TL;DR

• Moonlight's Alluring Crescent Moon is deceiving like Shadow Milk.
• Sea Fairy's Dread Trident of the Abyss is apathetic like Mystic Flour.
• Millennial Tree's Primal Mercy is Silent Salt's solidarity taken so far to an extreme level that it couldn't be considered solidarity anymore, it's self destructive altruism.
• Fire Spirit's Immortal Cataclysm is pure destruction like Burning Spice.