The Adventures of Jimmy Crikey: The Emerald Lake by Wallace Briggs

Jimmy Crikey is the orphan alien from Attalia who was born on Earth and chose to make his home in the magical lands of Roombelow.
Jimmy’s close friend Jade approaches the end of her apprenticeship with Matilda as a witch.
There are several challenges to complete before she can graduate as a fully qualified member of the sister’s Coven.
Jimmy is told not to help Jade directly. She must succeed in the trials using only her skills.
When collapsing roofs threaten the cave world of Lithnia, both Jimmy and Jade’s skills are needed to save Lithnia from the giant, rock-chewing beatles who originated in Egypt as scarabs.
The Sky Islands are caught in tornado winds, and a whirlwind is tearing the islands apart. Matilda instructs Jade to go to their aid. Jimmy is forbidden from interfering, but he does help Jade to carry out her plan to save the Islanders. Can the youngest witch overcome the danger?
Madam Coptra rules the Sky Islands and has given birth to The Weatherman’s, aka Lord Oron’s, son, Helios, and he must be introduced to the Coven of sister witches.
The dreaded Giant Scrabs return to their destructive chewing of rocks, which threatens the very structure of Roombelow, far away from Lithnia.
Jimmy and Jade trace the beatles resting place to a floating island in the Arctic seas. There the Centaurians, a race from planet Xe in the Alpha Centauri system, are seeking crystal diamonites from Lithnia to protect their world from gamma rays emitted by one of their suns. To save their planet, they would risk destroying Earth. Jimmy employs XRU, his talkative star ship’s navigator, to help the aliens and avoid an intergalactic war.
Matilda, the head of the four guardian witches of Earth’s realms, is called to move to a higher level. Who will she appoint as her successor?