https://www.skillshare.com/en/classes/blender-grease-pencil-combining-3d-and-2d-animation/1286211855

Blender is by itself an amazing free tool for 3D artists, but since they implemented Grease Pencil—a tool that allows you to draw 2D elements directly on the 3D space—it has become a must-know tool also for 2D artists. Using Blender Grease Pencil you will have infinite possibilities when it comes to mixing styles, 2D, 3D and anything in between.  This course will teach you the basics of Grease Pencil while we create together a helicopter that is partly 3D and partly 2D. We will go from modelling and adding texture to sketching and animating 2D elements on top of 3D. By the end of this class, you'll have mastered the essential tools and possibilities of Grease Pencil—making it the perfect starting point. Since we’ll move quickly through Blender’s 3D basics, some prior knowledge of the software may be helpful.