Step 11: Inside the head and below the eyes, draw a curved line similar to a letter U on its side for Rigby's mouth.
Step 12: Inside the U shape, at the top, draw three tiny arcs for Rigby's teeth. Draw a slightly bigger arc at the bottom for his tongue and another arc on the right for the side of his mouth.
Step 13: On top of Rigby's head, draw two small arcs similar to upside-down letter U's for the ears. Draw a few lines within the ear shape for structure.
Step 14: Use the top of the original rectangle shape as a guide to draw Rigby's head. Draw a set of wavy lines on top of the head for Rigby's bushy hair.
Step 15: Draw Rigby's arms by using the initial lines as a guides. Follow the basic path of the lines and make the shapes thicker. Draw a few curved lines at the end of each arm for Rigby's fingers.