This video is made by the Blender team and is result of 2D graphic tool named Grease Pencil.
They presents a 3 minutes short film showcasing Blender’s upcoming Grease Pencil 2.0.
This tool works like a pen in the 3D area.
At the end of this video you can see the combined effects of 2D and 3D.
Now, 2D and 3D animations benefit from advanced technology that complies with the basic animation rules.
You can see it on official youtube channel :