Assassin strategies?

[ano]

Yes, they will cast.
One of the most obvious (and reliable) usages of assassin for the early expansion is giving him a skull talisman with "cast spells" script. An assassin placed at the rearmost corner is capable of killing any simple commander without bodyguards and sometimes even with them.
Later it is a good idea to give an assassin an ability to summon something (Lifelong protection, Skull staff for a mage who has D1, Bottle of living water on so on). If an opponent flees, he is slain