Grave Guard stand on their own, with few character support, but lots of spells are required for them to outshine other elites.
Now, Black Knights on the other hand are not quite that simple. Having a Wight King or two with them is almost a must, as is giving them Banner of the Barrows. The other trick you'll need to master is having them March where they need to, and then rely on their M8 / Swift Reforms to out-maneouvre other units, which is difficult if the General of the army is not near, and only Vampires can have such mobility, not Necromancers.
Now, since they'll probably be out of range of basic Invocation of Nehek, you'll have to either abandon them entirely to their luck, or use buffed versions of it at the risk of miscasting.
Beyond that, they are a standard unbreakable cavalry with Killing Blow and ethereal movement. If you move them wisely, they'll do their job, but never as good as if they had a Vampire or two with them.
Now, Black Knights on the other hand are not quite that simple. Having a Wight King or two with them is almost a must, as is giving them Banner of the Barrows. The other trick you'll need to master is having them March where they need to, and then rely on their M8 / Swift Reforms to out-maneouvre other units, which is difficult if the General of the army is not near, and only Vampires can have such mobility, not Necromancers.
Now, since they'll probably be out of range of basic Invocation of Nehek, you'll have to either abandon them entirely to their luck, or use buffed versions of it at the risk of miscasting.
Beyond that, they are a standard unbreakable cavalry with Killing Blow and ethereal movement. If you move them wisely, they'll do their job, but never as good as if they had a Vampire or two with them.