Painting using only one watercolour pencil and a brush is the BEST WAY to learn how to handle your art equipment and shade and add tones and values correctly. I did a challenge about it on my Youtube channel - Painting an Elephant Using Only 1 Pencil - where I go in more details on how I achieved this

using a 6B Aquarelle Pencil (Faber-Castell) and a 6 Round Brush (Faber-Castell).

The choice of these two elements is critical to achieve a good result; if your pencil is not soft enough, you won't achieve really dark values, but at the same time if it is too soft it would probably be hard to have a variety of different grey values. On the other hand, if the brush is flat, you will be able to cover large areas (the body, the ear of the elephant in this case) but you won't be able to achieve small details. So before attempting this challenge, you should really think about what you've got and what the best choices are. (which will be the first important thing you will learn - familiarize with your art supplies 😇). Next, it is all about shading according to the reference photo and the anatomy of the animal/human you're drawing. Anyway, head to my Youtube Channel to hear the full story 🙌