[Verjigorm]

I had assumed that 100 was either hyperbole or a reference to Blood Slaves (which I was leaning towards). Why would you need that many?

1. Fielding 100 communion slaves is 100 castle-turns worth of production. You could have had 100 real mages instead which is a lot more powerful.

2. Nothing requires that many communion slaves, so if you have that many in a single group, you're wasting them and asking to be hit with Rain of Stones.

You should be able to defeat that Tart much more easily than that. In fact, you should be able to defeat several Tartarians with a good communion.

Let's see...

Dust to Dust
Paralyze
Soul Slay
Control the Dead (Great for large communions)
Enslave Mind (for Astral guys)
Charm (Nature guys)
Disintegrate (I've had very powerful SC's with excellent MR die to this spell. It costs only 10 fatigue and can be cast by a 2D mage. Even if he has a 95% chance to resist, if you cast it 30 times....)

There are any number of useful evocations that can kill most anything. Mages are very dangerous to SCs. There are very few SCs that can survive a large-scale mage assault. They're not invincible just very strong. With dudes that have lots of HP, protection, or magic resistance (usually all 3), look for things that ignore these bonuses. Does it have a weakness? Is it vulnerable to fire?

If there's lots of them Undead Mastery and Master Enslave but you need a rather large communion (though 100 is way too many. I think, if you're up against a large force they won't be GoR'ed, so you can probably work with 8 slaves).

When you get to go first cast Arrow Fend (which I think works on ROS) or failing that any basic armor spell like Legions of Steel.

If he's really, really, really nasty.... you can cast Horror Mark on him several times and then Call Horror or Send Horror if you have blood magic.

Marignon has Holy Pyre...

For thugs and SCs:

Herald Lance
Holy Scourge
Flambeau (comes with Holy Pyre so you don't have to melee and can use a more robust commander to attack)
Vision's Foe (Take out his eyes and he'll be useless)
Black Bow of Botulf (Removes his ability to cast spells)

Both of the bows, of course, only temporarily alleviate the situation unless you finish him off quickly. Since your opponent if fielding tarts, he can just drink from the chalice or wait for GoH to fix it.

Also, put penetration items on your communion masters:

Rune Smasher
Void Eye
Spell Focus