Warhammer interpretations
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The warp
An immaterial, highly mutable plane of existence mostly composed of psychic energy. The warp follows the movements of the material world, without subscribing to its physical constraints. Being composed of psychic energy, all living beings have a warp presence. Less well known, is that all matter has a warp "shadow" as well, neatly explaining why the warp moves with the material world. Empty space is occupied by the astral seas of the warp, while all planets are connected to the various warp lands, space twisting and folding from higher dimensions much like how a mobius strip would affect a two dimensional existence, only multiplied as to fit three. In the warp, travel is always done through both time and space, and thus distance is meaningless, and due to the aforementioned distortion in space, so is direction; intent and will are needed to actually travel, otherwise any movement is "idle animation" of both avatar and terrain and nothing is achieved.
The warp shadow of an object is less how it looks and more what it does, planets for example are the warp lands, only their spherical shape is not a function and thus absent. With enough skill, it would be possible to enter the warp and retrieve the warp shadow of a specific tool, bringing it back to material plane as a manifestation of psychic force, much like how daemons manifest without a true physical self in the material world. Such an manifestation would be a simple shape of idealistic function, a sword would be a rod with a crossguard and an infinitely sharp blade. A manifestation could be maintained so long as the object has actually ever existed at all. To actually affect the material to the idealistic degree would require tremendous amounts of psychic force however.
The machine spirit is an extension of this principle, as machines would also have a warp shadow. However even the most intentionally crude technology causes an over-defined warp shadow, that begins to exhibit traits of a cellular life form; extensive lists of catalyzed functions made very efficient. Computers, and indeed anything with any measure of information technology, has a warp shadow with emergent sentience, if often simple and dim. This is how warp drives and warp ships operate, the spacecraft itself intends to move through the warp, and the will of its simple sentience is catalyzed by the innumerable details of technology involved.
The C'tan known as Mag'ladroth the Void Dragon wised up to the abundance of energy in machine shadows, and consumed them with much the same vigor as the C'tan tricked into consuming each other by the Laughing God Cegorah. As a consequence much of the glorious technology of the Imperium, that it no longer knows how to manufacture, is beholden to the Void Dragon, who demands a measure of worship to permit functionality, for its eventual reawakening. The essence of the Void Dragon could not be split by the Necrons, and thus they instead split its prison; the moon-sized structure needed to seal it away was splintered into innumerable merely gargantuan monoliths that were then scattered across the galaxy on vectors left uncalculated. The Cult Mechanicus is unwitting of this subtlety, and indeed their veneration of the Machine God is seeded into them by the Void Dragon.
Technological weapons, such as and especially powerweapons, are points of interest for the Ruinous Powers. Combining the purity of purpose of the simplest tools with finely catalyzed functions to augment it, the warp shadow of a powerweapon requires trivial amounts of focus to devastate even the most stalwart fortifications in its path. There is some form of beneficial quality to be gained from the junction of a physical object to its warp shadow, but such secrets are well guarded by the daemons, and left to speculation by mortal psykers. The most common hypothesis is that a physical frame, no matter how distorted by the warp, anchors the warp shadow and wards it against foreign influence. Where the warp shadow of a sword could be interfered with by simple directed intent and will, a corporeal warp sword is like any other physical object to such petty tricks.
Energomantic Ecology
Inspired by warlock of the magus world
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There can be confusion of exactly how various environmental functions of existence operate in realities where all energy and elements can be quantified as energy particles. If a type of energy exists at all, it likely can be found naturally ambient somewhere. Black mana seeps into planes from swamps, and red mana from mountains, for example.
Ambient energies are important to measure by both quantity and activity; -25 degrees Celsius is perfectly comfortable in still air, but -5 degrees with even slight wind positively freezing. In worlds without such strongly defined energies, heat is most often a measure of molecular scale vibration and cold is a false measurement stemming from a lack of heat. In the reality cluster of the Magus Worlds, Heat is instead calculated from relative quantities of ambient fire and frost particles and their activity levels. Summer would be when fire is abundant and active, frost lacking and dormant, and Autumn when fire recedes and decreases in activity while frost does the opposite, and vice versa for the Winter and Spring. Daily deviations in weather and temperature arise from small variables causing localized changes to either the quantity of a specific kind of energy and or its activity, and thus a summer day with barely lowered temperature can feel positively chilly as the activity of fire decreases more than quantity for whatever reason, and the cold touch of winter can linger well into spring if the activity of frost doesn't recede as its quantity does.
In the Magus Worlds, there are multiple planes where a specific element is predominant over the others, a prime example being the Lava Plane. The Lava Plane has an otherwise standard "prime material" ratio of elemental prevalence, except for fire being more than triple what it should on average. As stone and earth elements are abundant in prime materials to provide ground to live on, the Lava Plane has oceans of lava and great reservoirs of magma where water would usually be, as the temperatures caused by the quantities of fire displace much of the water on the plane into a gaseous state.
With the abundance of fire energy it is natural that everything in the Lava Plane is inherently resistant to fire. Which can sometimes cause confusion as almost no other elements are wielded by the locals in their forms of magic. Why one would try to combat a lava worm with the discipline of Fire Plume is for the exact same reasons as one would bash at the skull of a bull with a bone club if otherwise unarmed. It might be more effective to wield an element the opponent is vulnerable to, but it is often more efficient to use the most abundant resources rather than try to get technical. The fire of an opposing warrior is still harmful even if you cannot burn; the energies oppose you and aim to disrupt your own even if you have no special vulnerability to them.
To remedy what could at best be considered a plothole, the weakening effect of the Dead Desert, we must simply consider the full implications of the new vector of activity. The ecology of the Dead Desert is deeply affected by the lingering ruin of a high rank battle having been fought there, leaving the area with the majority of its energy particles sinking to places unknown, and what being left much less than being more active to counteract being less. The area is almost as barren as a name such as the Dead Desert would deserve, but life yet thrives. Beings of powerful bloodlines, such as dragonewts (reptilians often known as kobolds), or vermin of inexhaustible will to live such as some species of rodents, thrive there to some equivalent of the word. Nevertheless the draconic bloodlines of the dragonewts will be forced into dormancy there, and every individual in a swarm of vermin will be even less than it should. Considering the apparent nature of the meditation techniques of the local magi, there is no validity to rest being less effective in the Dead Desert however. Magi cultivate their spirit and draw power not from their environment, but the uncolored mana of Unreality directly, as evidenced by the voidsky-like Astral Plane being immensely beneficial to their cultivation, yet highly dangerous with its vast energies. Thus the only manner in which the Dead desert could slow the restoration of a magus strength, is if it had an immensely obvious dimensional locking ward upon it to cut off the Astral Plane, which is in no way ever referenced. A more reasonable hazard would be that as the energetic body of a living thing cycles energy particles as if by breathing, the lower activity particles settle into them, and their own higher activity ones disperse into the desert beyond reach. This would overtime result in weakness and a sensation of fatigue, as the lower activity particles are less effective and clog the systems of the desert's inhabitants. In this manner even the magi would notice a seemingly inexplicable weakening of their proud strength, with inescapable feelings of fatigue, giving them ample reason to dub the area the Dead Desert.
As it is, while the active principle of energy particles is apparent from the description of the setting, it is never directly mentioned in story.