From Arcanum Illyria
An advanced assassin is a unit from the second tier of assassin units:
- For Humans, that's the Assassin.
- For Elves, that's the Night Shade.
- For Dwarves, that's the Deep Dweller.
- For Orcs, that's the Iqadron Acolyte.
As with other diplomatic types, advanced units are best suited to offense. That is, they have better offensive effectiveness per unit of upkeep cost than basic diplomats.