Merlin (Book 6): The Dragon of Avalon, T. A. Barron
Introducing Basil …
Long ago, at the dawn of Merlin’s world, a strange little creature named Basil appeared. Part lizard, part bat, his eyes glow with a mysterious light. When Basil discovers a threat to his world and to Merlin, he begins an epic journey that takes him from the Great Tree of Avalon to the outermost edges of the spirit realm. But his boldest journey will be to face his own deepest fears. And only if he survives can he save Merlin—and find his future.