At first glance, the classroom seemed to be an ordinary lecture hall.  The seats surrounded the podium in a semi-circle, each row rising three steps above the previous.  The students filling the seats were anything but ordinary.  A multitude of species from thousands of different universes sat, stood, bubbled, or whatever their equivalent of stationary posture, while they waited for the professor.

  The professor himself was an aged human in a white lab coat. His hair was grey verging on white and surprisingly full for the amount of wrinkles on his face and the curve in his posture.  His beard was short, cleanly trimmed, and just as grey-white as his head.  Reading glasses nestled in his hair obviously forgotten in his hurry to arrive on time to the class.  He coughed gently and the class quieted quickly.  "Greetings students to Multiversal Energies 101, I am Professor Erick Vaas.  Be aware this is a theoretical class, we will not be doing any actual conjuration or manipulation of energies.  If that was the class you were looking for, it's under Energy Manipulation 101." He spoke clearly as he looked over the class waiting for any to stand and leave.  After a few minutes of the students just staring back at him he harrumphed. "Ah good, the student counselors are doing their jobs, and you are all smart enough to ask them before joining the class.  Wonderful, perhaps I'll turn a few of you into true scholars yet." He turned to the board behind him and waved a hand, a piece of chalk lifting and beginning to write on the huge chalkboard, he spoke as the chalk clicked and scratched across the board writing the names of different types of energy.  "The multiverse is filled with innumerable types of unique energy.  Every god, archdemon, or elemental duke has their own 'unique' type of energy that is flavored by their history, will, and emotions.  For this first lesson, we will start with the six most basic elemental energies and their planes."  He turned back to the class, the chalk underlining each name as he spoke them out loud.  "Fire, Air, Water, Earth, Positive and Negative.   These are the 6 closest elemental planes to the vast majority of planes.  How close or far they are can and does vastly affect the environment of your unique material plane. Planes with close ties to their fire and earth planes tend towards large amounts of volcanic activity, a warmer core, and less ocean coverage for example."  He scanned the students waiting and, as expected, a centaur filly raised her hand timidly. He snorted.  "I do not stand on tradition over much lass, I appreciate you waiting to be called on but if I stop talking it means I am inviting inquiry if there is more than one student wishing to make a comment I'll call on you.  Otherwise, speak your mind." 

  She nodded and lowered her hand slowly, her voice was timid but the seat picked up her voice and projected it across the classroom startling her. "Professor I..." she flinched at the sound of her voice before continuing. "Professor I was wondering, my home plane is a majorly large plains with huge herbivores, we have very little in the way of mountains or oceans.  What plane would cause that?" 

  The professor smiled and nodded before speaking, "Assuming you don't have excessive rainy seasons, most likely a very close association to the plane of air.  Winds scour down mountains eventually, especially if the volcanic activity that birthed the land masses was not over-powerful, to begin with.  Planes with a close connection to air tend to be flat and expansive, you most likely have at least a moderate connection to the plane of water as well or you'd live on a desert plane." She nodded and settled back on the bench meant for centaurs. 

   Professor Vaas waited a moment more and then when there were no more questions he began to speak. "Most of you know or at least can imagine what the planes affect on your homes.  The planes most often overlooked are the positive and negative energy planes.  A Material plane too close to the positive energy plane will have mega-flora and fauna.  Monsters, animals, and people alike will tend towards larger batches of children.  Life spans are increased and old age is less detrimental to the health.  Sickness, somewhat surprisingly to early scholars, is more rampant as well.  Though fatalities from sicknesses are lower." He paused for a moment, waiting for comments or questions, then continued.  "The negative energy plane on the other hand tends to have less beneficial effects.  Animals, monsters, and people tend to be leaner and are less prone to disease but the diseases are almost always fatal unless they become a carrier. Childbirth is rarer, more difficult, and has a higher mortality rate. The biggest difference though, is the abundance of negative energy causes the spontaneous reanimation of the mindless dead much more frequently." He stopped here as the students flinched, hissed, growled, or any number of other negative responses.  He nodded, "Yes we are almost all in agreement.  Even the necrotic empires do not enjoy dealing with the mindless risen, they're a near-multiversal pest. An unfortunate reality that has cost the lives of countless beings.  Let us discuss why negative energy has this effect.  What is negative energy?" He looked around the room patiently.

  A student with pale skin and blood-red eyes started to raise his hand then stopped and just spoke. "Negative energy is the darker of the two emotional energies. Negative emotions create it and are empowered by it." 

  The professor nods and waits, but the student seems to be finished. "That is correct.  Negative energy creates undead by being attracted to the negative emotions emitted on death.  These emotions mingle with negative energy and then are absorbed by the body granting it its animating force.  Battlefields are notorious for creating undead because very little ambient negative energy is necessary when so much is generated by fresh death."

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  He waits for another moment and then continues, "On the other hand, there are a multitude of sapient undead who also need close proximity to the negative energy plane to appear and function.  Many of the harsh stereotypes placed on sapient undead are due to their reactions to low or negligible negative energy in their surroundings.  Ghouls hunger, Ghosts confusion, and Vampires thirst.  All of these are bad reactions to a lack of sustaining negative energy." He waited again, this time for the reactions of the students to calm down.  Students grumbled and muttered before settling again.

  One student shot to her feet though, a high elf with braided blond hair and blue eyes. "Professor, I object to this undead propaganda. Many have lost loved ones to the undead! we did not come here to hear sympathy for them!"

  The professor snorted. "If you feel sympathy due to my words, that's on you.  I am stating a fact.  Lack of negative energies causes the symptoms I mentioned, I do not weigh in on the guilt or liability. In point of fact, a lack of positive energy has a similar effect on living beings.  Elves for example begin showing signs of dementia.  Elven brains use positive energy to reinforce their memory pathways to handle their extended lifespans.  It's one of a multitude of tradeoffs they make." He stares down the elf until she sinks back into her seat. "Sapient beings are responsible for their own actions.  This is not a class on morality." 

  He adjusts the books on his podium and sighs before continuing, "We have discussed negative energy quite a bit.  Back on the topic of positive energy, how many of you were aware that positive energy can also be used to create a form of undeath?" 

  The whole class seems to be startled until the centaur speaks once again.  "I am professor, our tribal shaman calls our ancestors for guidance when making large decisions." She quivers nervously, some might consider this admitting to necromancy.  While necromancy isn't banned in the university, it is looked down on and stigmatized. 

  The professor smiles softly at her, "Yes dear, ancestor worship and some forms of medium use positive energy to awaken the memories of the dead.  These rarely lead to full manifestation unless a truly powerful spell or desperate need is used."  He looks across the class and then speaks again slowly,  "The major difference between negative energy undeath and the positive energy risen is that a being cannot be forcefully returned with positive energy.  It is antithetical to the energy itself and any attempt to forcefully raise or reanimate a body creates negative energy and negates itself. In contrast, forcing a creature to reanimate with negative energy against its will actually makes the reanimation stronger.  The fear and horror of a ghoul or vampire bite, or a mummies curse fuels the change.  Most sapient undead deal with low procreation rates due to their societal rules against forcefully changing others.  This is often offset with large rituals channeling negative energy into the participants of an attempted change." 

Behind the professor the chalk continued to write on the board, creating cliff notes of the lesson and underlining important points.  "Positive energy undead known as Risen tend to be short-lived and usually appear for an immediate need.  Positive energy tends to need a driving force to circulate, the need to protect, impart wisdom, or save.  Once the Risen no longer has an active and urgent purpose the energy lets go and dissipates.  Only a few truly powerful beings other than gods can fuel a Risen for long, and even gods can't force a Risen to continue existing against their will." he waved and a name was written on the board.  "Roland the Deathless was a positive energy conduit for a goddess of light.  His home world was very closely attuned to both positive and negative energy planes and was constantly embroiled in a proxy war.  An accident pulled him from his home plane to a different universe and he was cut off from his goddess.  His status as a positive energy conduit cut from a continuous source turned him into one of the first Positive energy vampires ever recorded.  He was able to pull the life force from living beings transform it into positive energy and grant it as healing to his allies.  His aura alone was strong enough to wick away the excess life force from living beings around him to fuel himself and some minor miracles. We still do not understand how he was able to so directly transform life force into positive energy.  It should be impossible, the taking of life force should be a negative act powerful enough to negate the creation of positive energy.  He was also noted as being able to convert his own life force into positive energy, and it's believed he may have used his body as a filter, choosing to sacrifice of himself to heal others as a sort of middleman."

  The students stirred at that, some looking in wonder, others in revulsion. one stood up, a middle-aged dwarf with a red beard. "An undead be an undead.  He were stealin' life from everyone and everything around him.  I'd have put him down." 

  The professor raised an eyebrow and nodded, "You are not alone in that thought, though it was later proven that he did not steal active life force with his aura but the passive life we naturally give off.  At the time there was a call to at least contain him.  The local adventure society stepped in, granting him sanctuary in exchange for his prodigious ability to heal.  He was later pivotal in the repulsion of a void incursion in the country.  His ability to siphon the life out of the void being and feed it to his allies allowed them to use powerful self-destructive skills for an extended period pushing back the void beasts." The professor sighed. "We are veering dangerously off-topic, but to return to the point. Positive and negative energy are two sides of the same coin, generated and needed by sapient beings.  A world lacking any negative energy would never produce sapient life.  a world lacking any positive energy would create only incorporeal mindless undead. The shadow plane is as close as any actually traveled plane gets. A hungry darkness full of frenzied shadow beings and nothing else." A bell began to ring and the professor nodded.  "We will discuss the shadow plane and other sub-planes next class.  Thank you for coming."