A note on using human remains:
(Disclaimer: I am not advocating for grave desecration or corpse desecration.)
Human remains can serve two different purposes in necromancy.
The first is that they can be used as altars or altar pieces, as they are imbued with Death's essence.
The second is that they can be used as powerful taglocks for summoning the spirit that previously occupied the body.
Using the remains as a taglock can also provide a great deal of power over the spirit, but this is not an option with cremation.
There are a variety of ways to execute both approaches, ranging from ceremonially complex to divinely simple.
The corpses themselves can be considered blessed objects, mediums, vessels, or even idols.
Wendell vs Tomekeeper's Death essence:
Wendell and Tomekeeper describe the energy or essence of Death in both overlapping and contradictory ways.
Wendell describes Death's energy as an electrifying spiritual lifeforce, melancholy, shadowy, yet deeply compassionate.
Tomekeeper describes death energy as sickly, decaying, destructive, absolute void, and fearsome.
These two approaches are not contradictions, and I think keeping both in mind can be helpful for a more holistic understanding.
However, running sickly, destructive energy through one's meridians and other lifeforce channels is described as courting disease.
Tomekeeper seems to believe that this is necessary for the sake of manipulating the energy directly.
If so, then emphasizing Wendell's healthier, more positive aspect of Death might be less dangerous in energy manipulation.
A note on ceremonial instruments:
Wendell and Tomekeeper both acknowledge that instruments are less important than the spirituality of the necromancer.
In Wendell's case, this is both about one's relationship with Death and one's proficiency in channeling his energy.
In Tomekeeper's case, more emphasis is placed on the energy work and Death is more of an impersonal force.
Instruments have still been used historically, often overlapping with goetic tradition.
Summoning circles, robes, and ceremonial weapons like swords, spears, staves, and wands are mentioned in a lot of grimoires.
Some grimoires even give details about how to prepare a body in order to use it as a conduit for a spirit.
It might be best to consider most of these to have more value as religious ceremonial symbols than practical tools for magick.
Corpses, bones, and rotting flesh are saturated with death essence and can be used as focuses for that reason.
Everything else is probably mostly aesthetic.
Death trance:
Both Wendell and Tomekeeper provide their own ways of seeking out Death's essence. These overlap heavily.
I also recommend a practice that is common to both Spiritualism and Greco-Roman Necromancy: the death trance.
Sleep is closely associated with death and spirit divination.
This is because deep sleep is often believed to be the closest the living can get to experiencing the peaceful rest of death.
Trance is a sleep-like state that is similarly associated with death.
Early Mesmerists had spontaneous spirit communications, leading to the practice being decried as "demonic."
From these early experiences, hypnotic trance induction became the foundation of Spiritualist "trance mediumship."
I consider this trance to be a mystical state of union with Death, and therefore a way to focus on his essence.
From this perspective, it is through the power of Death that trance mediumship works.
On "energy:"
"Energy" is a word that is used a lot in occultism, magick, and New Age spirituality.
It tends to mean something a little different to everyone.
The basic concept of "energy" is somewhat comparable to electromagnetism.
"Energy" can be channeled and stored like electricity.
Like magnetism, "energy" can be considered to be an invisible field or force that permeates all things.
A change in one place can cause a change in a seemingly disconnected one, through the invisible ripples of energy.
In Mesmerism, "animal magnetism" is said to be due to a "Mesmeric fluid," and these functions closely mirror what we call "energy."
Mesmerism was influential in occult and especially Spiritualist circles, which continue to use "energy" in place of "Mesmeric fluid."
Kardecism, a branch of Spiritualism, still expressly discusses Mesmeric fluid by name rather than call it "energy."
Mesmeric fluid has since been demonstrated to not exist in a physical or a literal sense.
Instead of Mesmeric fluid, the underlying effects of Mesmerist techniques are now attributed to suggestion.
Modern hypnotists have therefore mostly abandoned the concept while still building on the practices inspired by it.
Spiritualists have continued to use the language of Mesmeric fluid or "energy," since the concept was inherited with the tradition.
This "energy" is now often considered to be either a metaphor for suggestion or some kind of paranormal force.
As a paranormal force, it tends to be interpreted along the lines of Jungian-Platonic mysticism.
Energy exists in a Neoplatonic "realm of forms" that is treated as equivalent to the Jungian "collective unconscious."
Its effects on physical reality happen through the manifestation of synchronicity as meaningful coincidences.
This "realm of forms" conflated with the "collective unconscious" is sometimes described as existing on a separate plane of reality.
Wendell and Tomekeeper seem to imply this newer metaphysical version of Mesmeric fluid in their work when they mention "energy."
Useful terms:
A lot of the terms we use in magic are fuzzy and fluid; they can obscure rather than elucidate.
"Necromancy," strictly speaking, refers to a method of divination that relies on obtaining knowledge from the dead.
This is not necessarily confined to spirit divination, although that is the main implication of the word.
For example, it also applies to divination that uses corpses and bones, whether these remains are human or not.
Likewise, "necrolatry" can refer both to the veneration of the spirits of the dead and the worship of corpses as idols.
Necromancy and necrolatry can overlap, as they do in religions like Vodoun.
You can have necrolatry without necromancy, like how Catholics venerate the Saints without communicating with them.
You can also have necromancy without necrolatry, which is common in Spiritualism and European necromancy.
The worship of death itself is sometimes called "thanatolatry," which is a jumbled mess of a word compared to "death worship."
Due to the taboo nature of death worship leading to misconception, it has gained inaccurate connotations of suicide and murder.
Still, Death is venerated by a variety of incarcerated prisoners and violent gangs through Central and South America.
Some of them are murderers, but that's not because death worship itself promotes murder.
Also, "necromancy" is often confused with "nigromancy," which is a word for "black magic."
"Katabasis" is a descent or journey into the underworld.
The Afterlife:
In Spiritualism, mediums work primarily with two "places:" the Veil and the Spirit World.
The Veil overlaps with the physical universe or the "corporeal realm."
Ghosts, apparitions, poltergeists, etc. are said to inhabit the Veil, which acts as a window into or mirror of our world.
They have a limited ability to reach through the Veil for the sake of communication, as the Veil overlaps the corporeal realm.
The Spirit World has been described in a variety of ways by different Spiritualists, such as Swedenborg and Blavatsky.
Tomekeeper's description of the Netherworld seems to overlap with these concepts of a Spirit World.
In fact, I think the Netherworld is a more accurate vision of the Spirit World than descriptions of heavens and hells.
This potentially overlaps with the Christian concept of Hades and the Vodoun concept of Guinea.
Pagan underworlds in general could potentially be distorted descriptions of the Spirit World from shamanic katabasis.
Spirits residing in the Veil are called ghosts, while spirits residing in the Spirit World are called shades.
The Veil is said to "thin" on the day between the Winter Solstice and the Spring Equinox.
It also thins during "astronomical Samhain" which takes place on the day between the Autumnal Equinox and the Winter Solstice.
This thinning is said to allow spirits to transition easier between the Veil and the Netherworld.
It also makes it easier for spirits in the Veil to influence the corporeal realm.
This idea is inherited from Celtic mesopagan Samhain, adopted as Hollows' Eve by Catholicism, now popularly celebrated as Halloween.
The more culturally neutral terms for the Spirit World include "the land of the dead," "the Netherworld," and "the Underworld."