Kelsanor  

I killed Kelsanor yesterday with my level 42 reaver, backed up by a 41 cleric (35 enhance, the rest rejuv.) He is very tough. He can cast very high magic resists, and so at the start of the battle all spells are resisted. He can smite, DoT, and self heal too. He also seems to have a form of melee buffer as at some points I missed over 20 times even though he cons yellow to me.
When he is at < 20% health he would warp me down the hill side and start rebuffing and healing himself. I finally got him by life drain and constant DoTs more than melee damage.
Whilst fighting watch out for adds - which also conned yellow too.