Thing about demons is there are a ton of different [I]types[/I] or rather, species, of demons. For example, I created a specieis of demon called nightwalkers.

Nightwalkers are demons composed entirely of essence and the aspect of darkness/shadows. They can shapeshift into essentially anything they want, of any size, as long as they have enough essence, or just have evolved enough, to fuel the process. The average nightwalker can easily transform into say, a human, and with even a bit of skill/practice (or the like) they can change themselves into a form that is larger than a human as long as it's not like a building (as something of that scope would be limited to nightwalkers of incredibly high power...like perhaps a demonic lord haha).

There is no limit to the amount of forms they can have and aside from their Origin state (an ability they are inherently born with the potential to learn), which is a form that they don't [I]choose[/I] but can enter. It basically describes the very core of what and who they are. Aka, their personality shapes what the abilities and appearance of their Origin state will be.

If you want to make your own demonic race, with more limited shapeshifing, go ahead ^_^. If you'd like to know more about nightwalkers, I'll direct you to a link by request.