[K]

Baalz pretty much has it, but there are a few things he missed.

Storm Demons are less of a combat unit and more of a battle magic. Each tosses str-based AN lightning bolts(10 per battle) fired with Storm-immune Precision 14, so when you are rolling in with 20-30 of them you can have a devastating magical assault before you engage in melee.

Summon Imps is a great way to win assassination/failed seduction/deathmatch battles.

Agony is also a fear effect, so it has value beyond just weak attack.

Send Lesser Horror/Horror is a great way to add in killers with low amounts of resistance against high numbers of attackers. I've had more than a little success with casting a few of these and only having a few mages and no troops on defense to cast battlefield spells or other large area magics. Sheer probability means that the Horrors will attack the vastly larger force(barring Horror Marks).

Hell Power has a number of niche uses, so don't discount it despite it's great cost.

Infernal Prison/Claws of Cocytus are the best way to defeat Doom Horrors.