I will propose 3 specializations, 2 dps caster and 1 dps mele.
Dps caster full dmg: Summoning creatures and while they are active use shadow damage spells. ( maybe frost spells to slow)
Dps caster sticker: Diseasses and prejudices, damage over time and being able to take out some small creature
Dps mele: A mixture of the above, being able to take out small creatures, some damage over time spell and shadow damage abilities for the sword and frost to slow