The Mist Covered Mountain is a very haunting piece in A Dorian.
Normally it's played in the key of D, but Tony's arrangement is in the key of C, with a capo on the 2nd fret.
Tony talks about trying to arrange music so that it seems as if it's naturally written for the guitar.
There's a very nice version of this on DeDanann's album Mist Covered Mountain. It's available on eMusic.