Remember that an assassin can be only be in on-foot units. So don't fear assassins in the knights or dark riders ;)
i think you have the right of it here. magic something else and kill the champ who carries it.
Black horror, and comet and pit of shades only affects the terrain, and not units directly. Think about it like this, if you can't use magic...
The thing about it is, if you don't go magic then he spent 25 pts on a ring, and scared you out of that phase of the game. if he hides the ring...
yeah, kill his anti-magic ring with magic. nice plan you have there. o_O