Illusion = Dark Element?

Magical Attacks = Damage affected by Magic Attack

Physical Attacks = Damage affected by Weapon Attack.

I'm not sure where you get your sources, my boy.

He means that it's a magic attack-based skill with physical attack properties, because it's supposedly* affected by Darkness (which magic isn't affected by).

*I'm not sure if it really is affected by it, so I put a "supposedly" there.