Lucero by Maya Motayne

The thrilling finale to the #1 Sunday Times and Los Angeles Times bestselling Nocturna trilogy—a sweeping and epic Dominican-inspired fantasy about a face-changing thief and a risk-taking prince who must save their kingdom in the final battle between good and evil magic. Perfect for fans of Tomi Adeyemi, Sabaa Tahir, and Roseanne A. Brown.
In the aftermath of Sombra's return, the balance between light and dark magic has been destroyed and chaos has broken out in Castallan and around the world. Sombra's shadows have taken over to create monstrous versions of everyone Finn and Alfie love, and with war between Castallan and Englass looming, the prince and the thief must band together one last time—to save their entire world.
To stop the magical imbalance, they must find the stone relics of Sombra's body before the god can unite the pieces and regain his full strength once more.
But the laws of magic no longer apply, and with their own magic—and even the laws of time itself—drastically changing at every turn, Finn and Alfie are left on their own to stop Sombra and fulfill their prophecy before it is too late and the darkness reigns.
Will they restore balance to their world or will its light be gone forever?