Kind of embarrasing question...

[JaydedOne]

Maybe a few more details on what's going wrong? I don't have the demo but this is the first I've heard of blood magic just not working.

What nation are you playing, what rituals are you attempting to cast, etc. Perhaps zipping a turnfile and sending it up would also help.

[Archonsod]

Does your mage have sufficient level in blood magic to cast the spell? If you assign a ritual spell to a mage who either has insufficient ability or you have insufficient resources they will default to defend.

[UninspiredName]

Turn...File?

At any rate, I'm trying it with a Vampire Queen (What? I like summoning) pretender and the Gray Ones, (I think. The one-eyed crowd where the closest thing to a ranged attacker is a giant that throws boulders) five levels in blood and four in death. I tried summoning both a Barbed Devil and the undead fiend (I suck with names), with no success. Mound King worked fine.

[Morkilus]

You need three things to use rituals, like the barbed devil: researched the spell, meet the path requirement (as selected in the pretender) and enough blood slaves in the laboratory stash as listed in the spell. For battlefield spells, you need that number of gems or blood slaves in the commander's gem inventory (click on the rightmost inventory slot to assign).

[UninspiredName]

As I said before the caster's 5 Blood and 4 Death, Barbed Devil appeared under my ritual list, and the Blood Slaves were equipped to my pretender.

...Just making sure, you don't require more than 14 slaves to cast Barbed Devil, right?

[Nerfix]

This is strange.

[JaydedOne]

The blood slaves were equipped to your pretender?

Try dumping them back to the lab and casting the ritual that way. I don't believe (though I could be wrong) that you can cast ritual spells with components in individual inventories.

[Archonsod]

IIRC the blood slaves need to be in the lab stockpile rather than the pretender to cast a ritual.

The pretender's inventory is only ever used for spells cast in actual battle. Anything cast from the strategic screen uses the lab stockpile.