By @Chinthor:
In testing, however, they never drop demon wills. Even when under the soul snare effect, even when killed by a sentient sword, they drop none. Don't know if Vampirism needs to change how it identifies mobs, or if Blood Magic needs to update how it registers mobs from other mods.

I've researched what demon wills are, and for me it looks like that they should only be dropped by creatures that do not have a soul, and I think vampires somehow do have one.

Also do mobs from other mods drop them?

As far as I know (you'd have to ask WayOfFlowingTime or the code itself to be sure) wills can drop from any mob, but hostile mobs have am exponentially higher drop rate than passive mobs. In practice, hostile mobs killed while under "soul snare" effect or with a sentient weapon seem to drop around 1 in 3 or 1 in 4. Passive mobs drop them more like 1 in hundreds. Your mileage may vary.

As for mobs from other mods, that is harder to test in the current version of the pack. I just recently re-added "Ender Zoo" that adds Fallen Knights. They dropped wills in the past. We'll see about this version.

I took a short look at the code, but did not find anything related.
Since this does not seem to be a very severe issue, I won't continue to investigate this.

If you want this to be fixed/implemented please create an issue at BloodMagic repo and reference this one, I guess WayOfTime knows what I or they can do about this.
(Maybe it is relevant to know that none of Vampirism's creatures extends EntityMob)

the none of vampirism mobs is what make it not work it all so dont show up wind you use jounymap so you cant see the vampirism mobs on the map like you nomal o lee can

Closing this due to inactivity. If this still relevant, take a look at my last command