Mana, what is Mana? Well, Mana is a substance in my story Eye in the Sky which makes everything in the Hidden World possible. Without Mana, there is no Hidden World, no monsters, and no way for the entities to interact with the physical plane. 

Despite how important it is, people which include the entities(who some revere as gods) know very little about it. Yes, I as the author knows the origin of Mana and why it has so much power over reality. I even know the answer to the greatest mystery about Mana that people in Eye in the Sky try to find. "Why so little amount of organisms(like humans, animals, plants, etc) can use Mana despite there being near infinity amount of it. And why some just seem to gain the ability to use it seemly at random." Will people ever find the answer? Well yes but that's a story for later. 

Mana has 3 very unique properties that make it so strange, versatile, and powerful. 

1. There's a nearly unlimited amount of Mana: To people in the story Eye in the Sky Mana truly seemed infinity, as no matter how much is used more would takes its place. The only restriction is how long it takes for the amount of Mana in an area to refill. The more Mana-filled organism in an area, the more Mana will be produced in the area. Which in turn makes the monsters in the area stronger. Mana can be produced in two ways. 

• Area produced: Randomly a dense ball of Mana would manifest in an area, which is called a Mana Center. The Mana from the Mana Center would flow out and fill the area. Mana gets denser as you get closer to the Mana Center, farther you get thinner the Mana would be. This means that stronger monsters usually live closer to the Mana Center. Usually, Mana Centers are unstable and would eventually break down and stop producing Mana. The life span of Mana Centers differs from each other, one can last for centuries, while others might only last a couple of days. However, there are times Mana Centers lasts longer than its natural life span, which is when it develops an ecosystem. When the Mana that is radiated by organisms becomes greater than the amount that was in the Mana Center, it would start to stabilize and start to grow(bigger and denser) as it starts to absorb Mana rather than expel it. Areas, where this happens, are renamed as Mana Zones. Mana Zones are extremely dangerous as they house strong monsters. As the monsters in the Mana Zones get stronger, the more Mana the monster would produce which in turn makes the Mana Center grow more. The upside is, more Mana in a Mana Zone means more precious the materials that can be harvested are. The rate of growth differs from Zones to Zones. (Note: Mana will eventually start to decay, and disappear. But the decayed Mana is quickly replaced with new Mana)
• Organism produced: The Mana organisms produce is less pure, and usually is tainted by 1 or more elements.  However, they produce Mana at a higher rate then Mana Centers. When an organism produces more Mana then they could store, this Mana radiates out of them. It's this excess Mana that Mana Center's absorb and use to grow. (Mana inside an organism doesn't decay, but the Mana that they radiate does.)
  • More Information:
    • Elemental tainted Mana: Mana that is produced by an organism usually is tainted by an element, if an area has an abundance of element tainted Mana it's because of the organism that lives there, not because of the Mana Center. For example, if the Mana near a volcano has an abundance of fire Mana, it's because of the creatures that live there, not because of the Mana Center. 
    • Elements: 
      • Base: Fire, Water, Earth, Air, Light(Holy), Dark(Demonic), Corrupted, Decaying, Pure(Untainted)
      • Mixture: The base Elements can be mixed to produce new ones. For example: Water+Earth=Wood(Plant/healing) Mana, Light+Dark= Neutralizing Mana.

2. Not all can use Mana: In the long distant past Mana was at an even greater abundance, and every living thing could use it. However, because of an unknown event¹I as the author knows, and yes it would be revel at a later date caused organism to start losing the ability to store/use Mana. Now those that can't use Mana greatly outnumber those that can. 

3. Mana holds great power: Mana can turn an ordinary lizard into a 60ft monster that can raze cities. Humans can use Mana to cast spells that can almost do anything. For example, A common spell to fight monsters is Fireball. A spell that can make a ball of fire out of just Mana. A more grand example is the spell Creat Monster, a spell that lets the caster turn an ordinary animal into a monster.