Well, given that this is intended to be a bit of fun, rather than an in-depth study of the ethics of wish granting, I'd have to say Richard Thompson. He is a master of all styles of electric and acoustic guitar, a fantastic songwriter and can play very decent mandolin and tenor banjo. He has fantastic knowledge of so many genres and has a great sense of humour to boot. On the other hand, perhaps Martin Carthy. Or Mick Moloney. Or maybe Kevin Burke. Or ...