V.E Schwab 
Shades of Magic 
The Steel Prince #6

Prince Maxim Maresh has decided to enter a mysterious yearly magical tournament called the Night of Knives to prove his mettle. Open to anyone, soldier, pirate, thief or prince, the challenger must undergo four trials by magic designed to test – to the death – the strength, resolve, and heroism of the contestant. In all its history no one has ever succeeded in besting all four tasks, though many have tried and died…