The true propose of Mastermind in the arenas of the Ophidian Games isn’t clear as is illusions. But he uses and abuses his illusions inside and outside the Arenas. As an illusionist Mastermind loves to cause confusion to everyone, even to the Ophidian Lords.
He is an hybrid Demon / Spectral, and that may be the reason of all his destructives actions, as he never belonged to any of the races. What will Mastermind do next in and out the Ophidian Arenas is something that only his dark mind knows.