Step 11: Inside the shape of the mouth, draw two curved rectangle-like shapes on the top side for Donatello's top row of teeth. Be sure to include the gap in the teeth. Draw another curved line at the bottom for the lower row of teeth. In the middle of the mouth, draw a last curved line for the tongue.
Step 12: Use the main circle as a guide to draw the top part of Donatello's head. Follow the basic path of the circle but make the sides of the head narrower and the top a bit taller. Unlike his brothers who have circular and wider heads, Donatello has a thinner more oval-like shape to his head.
Step 13: Draw the rest of Donatello's face using the bottom part of the circle as a guide. Make the sides of the head come out a bit more to create the cheeks. Add a few lines within the head, under the mask for extra detail.
Step 14: Use the wavy line on the left as a guide to draw the first end of Donatello's mask. Follow the basic path of the line as you make the shape thicker. The end of the shape should end with a pointy tip.
Step 15: Draw the other end of Donatello's mask using the final wavy line as a guide. This shape should be under the other end of the mask, so be careful not to overlap the lines.