One version of this normal world is Tanion, the lost world of the unknown history. It is detailed in the separate appendix, as it is not part of the basic fantasy game system. Althought, bestiary, magicks and other parts of the RIP Fantasy are written with Tanion in mind, but they are easily adapted to any other world.
This mana can be trapped and channeled by skillful creatures into energy effects. This is usually known as magic, and practioners as magicians.
However, if the creature willingly allows a spirit to partially possess him, he usually becomes an avater for that spirit. In this coexistence, the creature has still his own thoughts and complete control over his body, but can get extra powers from the spirit living in him. However, sometimes this spirit may take more control over avatar body and control it for a while, but this is not very common. If the spirit is somehow banished, it usually returns after a while, unless destroyed.
Only some special creatures and magicians can enter or see the spirit world from the normal world. This place appears as a vague, dreamlike place of different shades of grey. The normal physical world reflects its creatures and objects into it as gray shadows, but travellers of the spirit world cannot affect them, but cannot move through them. However, if the creature in the spirit world travels farther, the shadows from the normal world start to fade and disappear, and ultimately, there is only a vast plains of gray fog. Unless the traveller returns, he enters deeply into the spirit world, finally entering some spirit realm. Those very experienced to walk the spirit world may enter the vast plains and then walk into another part of the spirit world, which is close to another place in the normal world. This way, it is possible to 'teleport' long distances in the normal world by entering the spirit world and then moving to place near the target location, returning to normal world there.
In addition to the spirits of the living, the spirit world has also numerous independent and free spirits. These spirits vary from evil wandering spirits to mighty god-like spirits living in their own spirit realm. These spirits usually wander alone in the spirit world, but sometimes can materialize into the normal world to affect things there. In addition, some of them has power to possess creatures or objects of the normal world, and most can be bind into objects to create magical items.
If either or both combatants are spirits without any material form from normal world the fight is usually fight of powers, as both can use their essence to create effects ripping each other and changing the environment around them. In a combat like this, willpower and general power is very important, while health and strength for those not natural to spirit world play a important part, too. Only special spiritual or mana-enchanted weapons may arm those natural to spirit world.
Demons are concentrations of all that is usually classified as bad or evil, feeding from that emotion and gaining more power. They itself have no power to enter the normal world and rarely can wander in spirit world, but magicians with known power can open gates between the known world and spirit realms, sometimes opening them directly into Abyss.
Death then takes the spirit and moves it to Netherworld, the realm of the dead. There it then wanders forever, until slowly fades away.