Step 15: Darken the right side of the guides under the eyes to create the top of the wyvern's muzzle. Make the shape a bit thinner than the guides. Add a couple of small lines at the bottom for the nostrils.
Step 16: Use the initial arc as a guide to draw the wyvern's mouth. Follow the basic path of the guide but make the muzzle narrower and draw a pointy beak at the tip. The line for the mouth should be wavy, and it should stretch all the way to the left.
Step 17: Darken the bottom part of the guide to create the lower jaw. On the left side, draw a spike protruding from the wyvern's jaw using a V-shaped line.
Step 18: On top of the head, draw two long horns using a series of curved lines. Sketch lightly at first to get the shapes right. The wyvern's horns should be pointy at the top. When you get the shape and position of the horns right, darken the lines. You can make these horns longer or shorter if you'd like.
Step 19: Draw more horns on the sides of the head using curved lines that come to a point. Draw a couple of horns along the left edge of the initial circle. You can make the wyvern's horns as big as you'd like or skip them altogether. Some of the horns on the right won't be visible because the head is turned, so just draw one small one.