The essence known as ectoplasm has its roots in the real world and mythology for a long time, attributed to ghosts its actually the coating of your cell's where all the important shit such as carrying stuff takes place away from the internal workings (powerhouse of the cell yadda yadda) for a shorthand description.
Incite the eldritch gods of a long lost (not dissimilar to wizards using the same medium or viral infections quite literally) religion to show favour, and now you have the seemingly magical ability to manipulate your inner life forces rather than just exclaiming (its magic bro, I aint gotta explain shit) under the diction and dark ways and teachings of the cult religion.
> Logically blood boil is a hostile reaction by agitating the 'ectoplasm' inside non cultists that are not attuned to damage the body.
> EMP is a burst of energy via the rune directly targeted outwards.
> Ghosts are raised by the raw energy contained within, as is the geometer summoned etc, and constructs are fuelled by RAW ectoplasm, a compound required to sustain life.
Blood is already required from within your own body to use many different blood cult interactions, so that as it may be can be left alone, however the actual essence of ectoplasm can be seperated from the body and this is where the suggestions come in.
Suggestions
> There be a methodical method to actually extract & detect the ectoplasm in blood samples, turning the blood into a clotted dead mess when seperated, cult members can do this without scientific equipment, and may onpurposefully raid medical supplies to steal excess blood bags.
> A new rune to overcharge the ectoplasm of a cult member rendering them with incredible speed and strength for a limited time, but slowly draining their blood if not constantly drinking ectoplasm.
> Ectoplasm is made into a liquid rather than a solid object and splatters with illuminating pink/reddish light, you'd require 10 reagent ectoplasm (easily scooped up from 30 units per thick splatter of a dead construct, and brightly illuminating footstep trails) to make a ghost burger for instance.
> Akin to the reasonable danger of eating carpotoxin laid fillets or spiderlegs, ectoplasm is made dangerous to consume with slight toxicity, but is easier put on the table for eating.
> You can heal shades/constructs and cultists (which cultists can directly help regain blood from ectoplasm via a hybrid minor heal & salbutomol effect) by giving them ectoplasm in any manner or kinds of forms, and cultist or those outright resistant to cult (ashwalkers etc) can use it without feeling the toxicity (though ash-walkers wont feel themselves healing)
> The internal supplies of artificers is to basically be a regenerating ectoplasm oozing depositor, injecting new ectoplasm into cultists, building outright with it or repairing.
> Cult metal and objects require a certain amount of ectoplasm to build, which can be gathered by substituting your own blood/raw extracted ectoplasm or by taking it from someone else
> When sacrificed, the body is deleted and all the ectoplasm is sucked into the rune to be sponged out later with a beaker/container, this is to make cleaning easier, as only bones will remain and leave a dry dead blood smear on the floor beneath.
Fun stuff
> A few more drinks and recipes requiring ectoplasm.
> A admin only plant (Booberry, as like the reference of the muffins which would directly require the muffin to use the plant produce instead of raw ectoplasm) that has concentrate ectoplasm within besides from a hallucination toxin & nutriments. Obtainable with silver slimes or by the podmen ruin.
> Special cult item, - Geometer scented soap, draws the ectoplasm out of blood that it cleans up, click onto a beaker to release.
TL;DR
Spoiler:
