[Manuk]

You can't count in assasins. as cool as they are they are meant more to kill researchers than commanders. He just have to bring basic 30g commanders and your assasin's turn is wasted and his army moved away from him.
Altough it would be nice to kill his priests. Unless he has some tough prophet or something for divine blessing instead of the common blessing.

How about lizardmen shaman casting curse to the giants.

Indy archers plus fire arrows.

Raiding devils.

Devils on hold and attack large enemy monsters (if the
commanders are bigger than the common giants this can be a sort of assasination).

Body etereal on vanguard?

dunno.