Step 20: Darken the original guide lines to create the shape of the unicorn's body.
Step 21: Use the line on the left side as a guide to draw the unicorn's tail. Draw the tail the same way as the mane. Follow the guide and make the tail into a solid shape instead of individual hairs.
Step 22 (optional): Erase as much as you can of the initial guide lines for a cleaner look. Don't worry about erasing all of the guides. It's okay to leave some behind. Re-draw any final sketch lines that you may have accidentally erased.
Final Step (optional): Add some shading to your drawing to give it more dimension and volume. Add the value lightly at first, then gradually build up to the level of darkness that you want. Pick the direction of the light source when shading so that it the shadows are consistent with it. Vary the pressure on your pencil to get different degrees of tonal value. It's a good idea to use reference from actual horse pictures to get the muscle structure right. Unicorns are mythical creatures, so you can add stripes or spots or even different colors to the body! Shading can be time-consuming, so be patient and take breaks. Continue adding the value until the entire body has the appropriate shadows.
Add a cast shadow underneath. This helps ground the unicorn so it doesn't appear to be floating. Don't forget to pause the video after each step to draw at your own pace.