Probably the piano. I'd have such a large variety of works to choose from, and if I could just magically play them well, I could amuse myself to anything I wanted at any time. No need for record players, great!

Harmonica. Great way to relax.

I'll take eight!

I think I'd be highly suspect of that being and probably would tell it to go back where it came from and stop bothering me with its trivial conundrums. If that being wants to play games, away with it I say.

As for musical instruments, I think I am most fascinated with a piano, followed by saxophone and maybe cello or violin.

Mandolin. If I wanted to gain at least enough skill to play an instrument without practicing, I'd want to learn the mandolin. I love how they sound. As much as I'd love to be better at death growling, the mandolin is somehow the instrument that I like the most.

guitar without a second's thought.

i svck at the guitar (and i've been playing on-off for over 20 years).