Hey, here's where Dirtifer came from. I was actually really surprised to see a dockalfer show up in Wizard School Mysteries Book 1, I think I designed him before the book was released? Related was my attempt to draw a Beelzebub to varying results.
Most of this page is dedicated to the knucker and Lambton worm. The knucker was designed after seeing the kettles and pot-hole lakes named after knuckers. It made me think of them as a type of pest which lodges themselves into these holes, with spikes to prevent people from removing them. Their ears also have long scales or hairs to mimic reeds. The Lambton worm was drawn to make it look a little more like an eft, or juvenile newt, which the worm was supposed to resemble.
Finally at the bottom, Drake lets his hair down, to the admiration of his friend. We'll see more of her on the next sketch page, but she's part of an extended friend group, a "TDG Junior" if you will. Fun facts: her name is Angel and she predates both Ariel and Drake!