The main elements in the mana world are:
Every element has one element it is strong against and one it is weak against. These relationships form a circle:
- Fire is extinguished by Water
- Water is absorbed by Earth
- Earth is eroded by Air
- Air is consumed by Fire
Then there are four sub-elements:
Metal (Fire and Earth)
Plant (Earth and Water)
Ice (Water and Air)
Elemental Effect on damage
Elemental damage is mainly inflicted by magic attacks and magic weapons. Normal weapons inflict damage that is not modified by elements.
Every being has an elemental damage modifier for each element. These modifiers are percentual modifiers that are applied to the elemental damage the being receives before the damage reductions by physical or magical defence are applied.
The system allows "composite damage" attacks of unelemental and different elemental damages. When a being receives a hit by an obscure multi-elemental physical attack that gives 100 unelemental damage, 50 fire damage, 50 water damage, 50 air damage and 50 earth damage, each elemental part of the attack is modified individually. The results are added and then processed as one attack by the other damage calculation mechanics.
Elemental modifiers of player characters
The elemental modifiers of player characters are influenced slightly by its race and mostly by its equipment. They can also be changed by temporary status effects.
Every piece of defensive equipment that has an elemental property lowers damage received from the element it is strong against but, on the other hand, increases the damage received from the element it is weak against by an equal factor. This means that every resistance against one element is cancelled out by an equal weakness against another element. A "rainbow equipment set" that mixes pieces of all elements results in no resistance at all because all the resistances cancel each other out. That way a character can never be completely invulnerable.
For calculating these resistances and weaknesses, every defensive item with an elemental property has an elemental property modifier that is a decimal number usually slightly larger than 1.0. All elemental damage of the element it is strong against is divided through this number and all elemental damage of the element it is weak against is multiplied with this number. The elemental property modifier is communicated to the player in the item description as a percentual modifier on both elements to make it easier for the player to understand the effect of the item.
This system only covers the 4 main elements. The combined elements, lightning, metal, wood and ice, aren't covered in it yet.
- Example: A mage robe of earth would, in addition to raising the characters earth magic skill, have an elemental modifier of "Earth 1.25". This means it lowers all received water damage by 20% (100% / 1.25) but increases all received air damage by 25% (100% * 1.25).
All elemental damage modifiers are applied one after another. This means that the total elemental modifier of a character is the multiplication of all its elemental modifiers. As long as there are no items with an elemental modifier of 0.0 no total elemental modifier of a character can reach 0 and thus grant complete immunity against an element. And such items should not exist as they would result in a division by zero when calculating the damage of the element it creates a vulnerability for (infinite damage?).
- Example: A character wears two very powerful water items with a modifier of "Water 2.0" each and thus has two times a 50% resistance against fire and two times 100% more damage by earth. This does not result in 0% fire damage but in 25% fire damage (0.5 x 0.5 = 0.25) and doesn't mean 300% damage by earth but 400% damage (2.0 x 2.0 = 4.0). In other words, when stacking elemental modifiers, they are multiplied by each other (cumulative).
Damage Modifier(element) = 100% * EP(element+1) / EP(element-1) EP(element) = product of the elemental property modifiers for the element.
Elemental resistances without coupling to an elemental weakness
Equipment pieces or status effects that modify the resistance against one element without affecting the others (think "asbesto jacket" for fire resistance) are thinkable but should be rather the exception than the rule.
Elemental modifiers < 1.0
Elemental modifiers smaller than one would result in less damage by the element it is weak against and more damage by the element it is strong against. Such items are technically possible in this system without any problems when the content designers need such an effect.
Elemental resistances and weaknesses of monsters
I think we can take the freedom to set those arbitarily. In case of monsters that are clearly the incorporation of a specific element we should stay by the rule "strong against following element - weak against preceeding", but in case of other monsters we can set the resistances as they seem plausible to us (a hay golem can be vulnerable against fire without being invulnerable to earth, for example).