He patrols the graveyard from Thalnos' crypt to the hallway you enter the graveyard from. He has a Lich Slap that hits for roughly 800-900 shadow damage on his target. He also has a Frostbolt Volley with 25-30 yard range (can easily be ranged by healers). In addition, he channels a Mind Flay for 150 shadow damage per tick while attacking. He also has a Frost Nova that hits for about 130-150 damage and immobilizes.
It's best to pull him down the stairs and into the last hallway before the graveyard. Have your warrior tank him with his back to the wall at the end closest to the stairs, with your healers standing at the other end in range of heals but out of Frostbolt Volley range. Be sure to keep the tank topped off because the Lich Slap is quite powerful.