Labyrinth of Fire (Island of Fog, Book 2) by Keith Robinson
In the sequel to ISLAND OF FOG, the young shapeshifters have made it safely into Miss Simone's world. Some of them are looking forward to meeting their alternate kinds. Others dread the prospect.
Dewey, for instance, quickly feels the pressure of being a centaur. Miss Simone and the villagers make use of special energy rocks to power homes and advance technology. But the superstitious centaurs are convinced that the mining of these rocks incurs the wrath of Mother Nature, and demand a return to an older, simpler lifestyle. Meanwhile, the village in the north is under constant attack from harpies and dragons, and the villagers desperately need help.
Hal and his friends join forces to deal with these serious issues. Together, with their individual talents, they can conquer any problem... or so they've been told.
They end up in the heart of dragon country, down in the Labyrinth of Fire beneath an oozing volcano. Their quest forces them to question the extent of their shapeshifting abilities, and this leads to a shocking discovery that is likely to start a war.