The Prodigy, book 1: Dark and the Boy in the Hole M.A. Batten

Having been imprisoned in a deep stone pit by the tyrannical King Baltus for as long as he can remember, the Boy With No Name is unexpectedly set free by the last living minotaur, the albino Grim. Together, they escape into Myrr Wood to join the few remaining monsters of the Old World – a ragtag bunch of goblins, trolls, bendith, harpies, a wendigo, and the only lykkan left in the realm – all hunted by humanity to the brink of extinction. When the Nightlings discover the boy can mimic anything he sees, including their own fantastic abilities, they are ready to follow him in an uprising against the world's greatest evil: mankind. However, there is a traitor among the Nightlings, traps have been set, and the King has a deadly new weapon that could wipe out the creatures of the night once and for all. War is coming. But first the boy must decide if he is human, or monster.