I have a student at want to create a Sprite that is a rectangle or octagon. Can they create these type of sprites or are they are ready made somewhere?
They certainly could be drawn inside the editor or a simple image could be uploaded into the editor. There is a rectangle tool inside of the Animations tab so for a rectangle, that would be great. For other shapes, you could find a shape from somewhere like pixabay.com (images that are free to use of most purposes) and upload it there.
Does this help?