Image imported from derpibooru 
Original Description:
 
Celestia and Luna are a unique pair of engines as they are the first steamtures (steam creatures) to be created. Shortly after the dawn of steam, Equestria was trying to find ways to make their new steam engines as useful as possible. Then one day, someone had a crazy idea; “Let’s turn our strongest workers into steam engines.” Knowing the many ways this spell could go wrong, it was agreed that the only ones that would be capable of making living steam engines would be alicorn-level magic, such as the two engines you see here.
 
Many of these steamtures have a lot of abilities that normal locomotives don’t have. These include being able to move by themselves, bodies they can bend in a way metal would normally break and extendable wheels they can use like hooves or whatever appendages they have. They also have the ability to change back from their steam forms to their regular creature forms at will, similar to the turbo teen. Additionally, while in their creature forms, the food they consume becomes the same as coal for their steam forms.
 
With many of these new steam engines being incredibly versatile and there are times when you can see one of the royal engines taking a train once in a while.