Well, last thing first-the secondform would be the 'Super Giant'
'Darkvision' because he can detect radiation, 'Starfires', because he's the Prince of Space (I was thinking he'd get the power from his spaceship, but a wand weapon works, if you'd rather not give him magic)
And I suggested giving the human-sized "Prince" version magic and flying, and not giving the 'Super Giant' version flying, because it would differentiate the two forms from each other, making each viable in different circumstances.