The health bar is a vital meter that shows how much damage the player can take before death ensues. Health can increase in multiple ways, which are from leveling, getting items, or other less common means.
Health can be restored by some class abilities, eating food found in certain structures, or by waiting for the player's health regeneration to bring it up.
Mana is used for casting spells or skills that aren't the primary attack mode.
Increasing the current mana level can be done by picking up crystals lying around or by item effects.
Armor is used to reduce certain types of physical damage. Resistance is used to reduce certain types of magical damage. For the sake of brevity, both will simply be referred to as armor. The formula for calculating damage reduction = 1 - 1/(1+armor/50)
Different sources of damage reduction will stack multiplicatively.
When playing in NG+1 and beyond, your character receives a debuff reducing his Armor and Resistance. This debuff scales with each level of NG+.
The exact amount of armor/resistance lost can be calculated using the following formulas provided by Miss:
For example, a character in a NG+2 game will receive a penalty of 84.09 armor and 67.27 resistance.
Note that armor and resistance can become negative when this debuff is applied, resulting in increased damage taken.
This is a figure to show just about how much damage you can take from an enemy total before dying. There are two kinds of Effective Health, Physical (EPH) and Magical (EMH) both use the same formula, the only difference is whether you're using armor or resistance to calculate it.
Effective Health is calculated with the following formulas:
Effective Physical Health = Health*(1+Armor/50)
Effective Magical Health = Health*(1+Resistance/50)
The reason there is no overall "Effective Health" stat, is because the number it shows would be the average of the two, which is inaccurate to your actual effective health. As an example: A level 1 paladin, has 90 EPH, and 75 EMH; that would average to 82.5 Effective Health, but if you take 82.5 Magic damage in a single instance, you die, because your EMH is only 75.
Evasion is calculated similarly to crit chance, where each source of evasion is NOT additive. Rather, each evasion source rolls independently for evasion and if any one of them rolls a positive outcome, all damage will be nullified.