That's some great boss music lol

Not give the hero a chance to attack.

I'd just cover myself with THAT unbeatable enemy that you cannot touch.

Remember that one part in Eternal Darkness where your character built up all of this power to take on the final boss, walked into the chamber, and was instantly turned into a splatter on the floor?

Well, I'm nothing like that. You'd walk into my chamber and I would be in their masturbating. Then, I'd glance up, see you and die from embarrassment.

You win!

I will be able to create illusions and mentally transmit pain without physical damage. I will have teleportation skills(at the very least super speed) and the ability to manipulate electromagnetic waves. Yes, that means lasers, magnetism and cosmic blasts. Also means I can see things the naked eye can't. The stage will be high in the skies so the hero better find a way to fly for this fight even if he can't fly normally.

I'd go with psychic BS goes through relic boss status effects, combined with regeneration to try and force the party to kill off each other and stall each other to the point of where the surviving members damage output is less then my regeneration.

Music wise i'd go for something pretty minimal and spooky actually....

arena would probably be some weird cliche wavy type area that changes every few rounds to represent different mindscapes and the situation.

I would harness the power of horrible singing and base all of my powerful attacks with that, absorbing my energy from Rebecca Black, Justin Beiber, Ke$ha, and the girl at :11

Believe me, I've been. And I didn't have mercy.

I am a game without a final boss.

And btw, only stupid villains (the great majority of them) leet the hero reach his personal room. An efficient villain, faithfull to his ambitions would just trow the protaginst in an endless chasm of flaming death instead.