[Baalz]

Blood magic can be very effective in combat. As Jazzepi points out though there is a higher bar to use it as you'll only do so in the fights where it makes sense to burn gems. With that in mind, here's some suggestions:

Summon imps + bloodlust is a very nice little combo to pull off with a bunch of cheap research mages and modest research. It's surprisingly effective in many situations. They're flying so they'll tangle up archers and mages, they're size 1 with 2 attacks so they'll overwhelm high defense, they do decent damage buffed, they have a good defense so they've got a bit of staying power in numbers, and they're fire immune so they're a perfect screen to drop fire evocations on or to tie up that fire brand wielding SC.

Bloodlust & Rush of Strength can be worth the price of admission all alone depending on what you're fielding.

Bloodletting is one of the easier battlefield wide spells to cast and you can keep casting it because it reinvigs you. One casting of this spell is a bit underwhelming, having 2 guys cast it several times though...20 blood slaves is a cheap price for killing a large army.

Blood rain - fabulous for use in combination with other fear effects. Panic, terror, starvation, horrors....even super-elite forces have a breaking point. I think this is an underrated spell, you know how easy it is to break those 8 morale militia? Well in my dominion your 13 moral elites now break that easily and horrors have a *huge* fear aura.

Call horror - a bit of a niche spell, but it's not too hard to find situations where 2-3 horrors will really ruin somebody's day even without counting on their fear. With horror marks it's not too difficult to point them in the right direction either.

Reinvigoration - people keep this one in mind for communions, which it's great for, but it's also very worthwhile to have SCs/Thugs at 0 fatigue before going into melee, and it can allow you to cast those big spells several more times.

Hellbind heart is like charm with a much larger range and easier path requirements.

Leech is one of my favorite spells. Easy requirements, AOE1, no way to get resistance (unless you're already lifeless), AN. Not only is it perfect to counter most SCs, you'll be amazed at how fast 20 triple blessed whatevers evaporate before they can even close on your PD if you get 4-5 (cheap!) casters to spam this.

Life for a life + go to hell - The best anti-SC spells in the game.

PS wounded blood slaves are definitely usable. You can easily witness this by casting bloodletting several times as it effects your slaves.