[Boron]

You have to evaluate if you prefer defense from Ghost Riders or normal defense .
In games vs. the AI normal defense is often better but in MP you need castles vs. Ghost Riders , Horrors etc. otherwise it is too annoying .

Unfortunately Ghost Riders are really rather cheap and easy accessible for all Nations . Just 25 Deathgems for a new Demilich and you have another Ghost Rider caster .

Expect your 1-2 Main Armies Ghost riders can kill almost any of your armies/SCs . But there are also the Artillery Spells like Flames from the Sky .

That combination forces you to only use Devils + Mech Men if you can do so .
Everything else either dies to Ghost Riders or the Artillery spells .
If you have a few turns time , e.g. you have lots of castled lands , then with a combination of the following spells you normally can wear down (almost) any army :
Leprosy
Beckoning
Mind Hunt
Earth Attack/Ashen Angel
Ghost Riders/(Lesser) Horror
Flames from the Sky/Murdering Winter

And then there are the Battle Spells like Rain of Stones , Earthquake and Wrathful skies which reduce the army reliable down to SCs + Air immune Troops .