Arcane Bolt: 2sec casting, about 14,000 arcane dmg. He always spams it to whom have a highest aggro except when he casts nasty Flamestrike.
Blizzard: Instant (?) casting, deals 3500~4000 frost dmg per 2 sec in 10 yards radius. Lasts 10 sec, and he uses this spell every 10 sec.
Flamestrike: 2sec (1.5?) casting, deals about 3500 fire dmg in 10 yards radius. And if you step upon flamestrike zone, you'll be molten down. (It seems to this nasty ability dealing about 4000 fire dmg per sec.)
Dampen Magic: Nethermancer will casts this spell upon himself. Makes him taking only 25% dmg from spells, and reduces healing done up to 500. A mage will spellsteal this from Nethermancer and tank him.