Names: Celestia and Luna  
Species: Sun and Moon Ponymon  
Type: Light/Cosmic (When fused together)  
Ability: Magnetic Flare - Increases the power of  
Fire-Type moves but heals the user if hit with a  
Water-Type move.  
Gmax Move: Gmax Eclipse - Cancels any weather effect.
 
PonyDex Entry:
 
When their powers are combined, Celestia and Luna can create a portal that  
leads directly into the heavens. They can only achieve their Gigantamax form  
when they work together.
 
Origins: Celestia and Luna are a reference to the Greek deities/siblings  
Helios and Selene. Their wings forming a portal into space is also a  
reference to the titan Atlas, as well as the two pillars put in place  
by Hercules.
 
NOTE:
 
So I decided to go in a different direction with the sisters.  
Originally I was going to give them their own individual  
Gigantamax forms, but I thought it would be more fun  
to combine them into one form, similarly to Twilight and  
Spike. For this reason, the Gigantamax Celestia that I  
had posted before was deleted.