resources:

hit points (HP)
mana points (MP)
stamina points (SP)

regular stats:
strength (STR)
dexterity (DEX)
vitality (VIT)
magic (MAG)
faith (FTH)
willpower (WIL)
charisma (CHA)

should all be self-explanatory

atk = raw_atk x skill_modifier x (100% + crit% + weakness%) x (100% + misc modifiers)
def = raw_def x (100% + def modifiers) / (100% + crit%)
dmg = atk x atk / (atk + def)

skills adjust atk before the formula
criticals by default add +100%; are not chance-based, you have to hit the right spot
weakness modifier depends on the skill granting the weakness

resistance reduces atk by the resistance rank (level of class or title or whatever that gave it), not below half, and adds the same bonus to def

if defense is 5x atk or higher and the attack did not hit a weakness, the attack deals no damage

physical attacks use STR as raw_atk and VIT as raw_def
magic attacks use MAG and WIL
social attacks use CHA for both

The simplest thing to remember is: if atk equals def then damage is half of atk.
Past that point, the effectiveness of def quickly drops off until you hit the immunity point.

This formula has the quirk that def becomes more effective point for point the more damage comes your way.
However it also kinda nerfs multi-hit attacks.

Examples:

100 atk vs 0 def:
100 x 100 / (100 + 0) = 100 damage

100 atk vs 100 def:
100 x 100 / (100 + 100) = 50 damage [50 points of damage absorbed]

200 atk vs 100 def:
200 x 200 / (200 + 100) = 133 damage [67 points of damage absorbed]

100 atk vs 200 def:
100 x 100 / (100 + 200) = 33 damage [67 points of damage absorbed]

100 atk vs 499 def:
100 x 100 / (100 + 499) = 16 damage [84 points of damage absorbed; 2.5x def and damage is only halved]

100 atk vs 500 def:
excessive def = no damage

double hit 50atk vs 100 def:
2x (50 x 50 / (50 + 100)) = 2x16 damage

double hit 65atk vs 100 def:
2x (65 x 65 / (65 + 100)) = 2x25 damage

100 atk vs 100 def critical:
(2x100) x (2x100) / (2x100 + 100/(100%+100%)) = 200 x 200 / (200 + 50) = 160 damage

Regular weapon attacks cost 30 SP and use 100% atk.
Spells take about 3-5 seconds to cast.

Spells can be "created" on the spot within the limitations of known affinities and skill ranks.

relative to a Rank 1 spell:
Rank 0: 0.7x cost, 0.25x effect (atk, status rate, ...)
Rank 1: 1.0x cost, 1.00x effect
Rank 2: 1.3x cost, 1.25x effect
Rank 3: 1.7x cost, 1.50x effect
Rank 4: 2.2x cost, 1.75x effect
Rank 5: 2.8x cost, 2.00x effect

rank 0 damage spells can only be a single projectile with no extras added

example shapes:
single projectile: 100 MP, 200% atk
five projectiles: 115 MP, 5x65% atk
line piercing projectile: 120 MP, 130% atk
area damage (10 ft / 3m diameter): 145 MP, 110% atk
rain (130 ft / 40m diameter, 2 minutes): 1000 MP, 5% atk - to make it not too OP lets say it only delivers 120.000 "hits" even if there are way more drops (1000 per sec over the whole area)

can add status chance: add 30 MP cost, rate 40 x attack modifier of base (e.g. 80 for single projectile)
the status effect must match to spell element, e.g. burning for fire
rate is halved for effects that take away control like stun or charm
status rate is only affected by spell rank on non-damage spells

Spells generally use MAG for damage.
Holy magic uses FTH instead and has its atk reduced to 5% if the target is not weak to holy.

Healing effects heal 100% FTH, cost 500 MP (if spell) or 700 SP (if skill) at Rank 1 (same Rank scaling as damage); aoe healing does NOT exist, nor does revival

These spells can cure either HP or "status damage", or both partially.
E.g. when an enemy lands a fire skill for 1000 damage which then triggers a burn status effect, this status effect is worth 1000 HP which needs to be cleared before the burning goes away.

When using healing magic on an undead target you can choose to instead harm them; in that case, treat the spell as a non-elemental 400% FTH spell (Rank adjusted).

Spells require the relevant skill with the respective rank to use.
Some caster classes have a range for their magic skills, e.g. "Cure Magic Rank 1-3", in that case, every 15 skill levels in that skill increase the available magic rank by 1 up to the listed maximum.

So in that example skill, skill level 1-14 is Rank 1, 15-29 Rank 2 and 30+ Rank 3.
Acquiring a higher Rank does not prevent the use of the lower-ranked, cheaper spell version.

However, MC's "god's lost child" title sets those to Rank 1, with no exceptions.

Rank 1+ spells require the respective skill to use, Rank 0 spells can be used with either the affinity OR just having MAG >= mp cost of the spell.

Spells without the relevant affinity cost x2.5.

Rank 0 spells also include e.g. household spells, [appraise] for 300 MP and a "warp home" spell for 2000 MP, however, the latter is space type which no one gets by default; you either need a massive 5000 MP or one of the relevant classes.

Space magic encompasses storage, transport/teleport effects.

Teleport Rank1: 2500MP; teleports up to (1+MAG/1000) willing targets; need to have visited the target location.
Max distance is MAG x 33 ft [10m].

Rank modifiers apply to the max number of targets and distance.

Healing, buff and debuff spells are only available at Rank 1+ and require the relevant cure/holy/curse magic skill respectively.

mostly normal/damage elements:
fire, ice, lightning, wind, water, earth, poison, light, dark

special types:
curse - does not inflict damage, only used to inflict status effects
holy - as normal elements but non-weakness attack power is 5% of normal
sunlight - generally only inflicted by the sun, only affects those with appropriate weakness (mostly undead) and ignores defense stats

A stereotypical appraisal is available to everyone in the form of the typeless [appraise] spell for 300 MP per use.

It does NOT reveal titles unless the target explicitly allows it.
It always shows regular classes and race.

After that it follows 3 rules:
1) if user and target are "friendly" with each other show level and stats, skip 2 and 3.

2) if at least one of them is hostile to the other you can see stats with [appraise] if the user is significantly stronger than the target - MC's [World Navigator] title breaks this rule

3) if the target could see all of your stats with [appraise] you only see levels and stats as “?”

Extra races (e.g. vampire) only show the base version (vampire lord only shows as a vampire).

To be honest, I'm not sure what to do with special weapon techniques without it becoming a complicated physical mess, so for simplicity's sake, they just use the default attack power and cost per attack motion independent of technique.

E.g. a triple stab costs 3x regular attacks worth of SP (3x30 = 90) and deals normal damage per stab

Skills can have one of the following cost types:
1) Just use MP (spells) or SP (skills).

2) x uses per day, in that case, they typically do not cost additional MP or SP to use

3) upkeep skills reduce the max of the respective resource while active, e.g. "upkeep 200 SP" reduces max SP by 200 while active.

4) Concentration skills cost no further resources but you can have only one concentration skill active at a time.
Concentration can be broken; in that case, you can't reactivate a concentration skill for 3 minutes.

atk: mind effects use CHA, other MAG
def: mind effects use CHA, other WIL
chance = base rate x (1000 + 5x level of triggering skill + atk - def) / 1000

If the chance is below 10% it auto-fails.

Monster use their total level instead of the level of the triggering skill.

Resistance reduces base rate by half of the resistance level (level of class or title that gave it), not below half, and adds the full level to def.

For the sake of resistance count both a resistance to the specific status and a resistance to the element of the triggering attack.

Mind effects take circumstances into consideration; if someone is already (non-status) afraid landing a fear status becomes near guaranteed.

Status effects scale with the (simulated for non-damage spells) damage of the triggering skill (=status damage).
When applying a status effect a second time, the timer resets (if any) and the status damage is summed up.

E.g. poison deals 0.2% of status damage as HP damage per second, so if a poison skill does 1000 damage it would deal 20 dmg/s.
If then a second poison skill lands for 500 damage the dot increased to 30 dmg/s.

Some status effects have a chance to chain into a different chance, in that case, the new status gains half of the status damage.

Generally, status effects do not wear off naturally and need to be either properly treated (healing spell or medical treatment as in real life) or in case of mind effects have a chance to be shaken off.

status effects so far:
bleed - 0.1% of status damage as HP&SP damage per second
burn - 0.1% of status damage as HP damage per second; has a chance to inflict panic every second
charm - views inflicter as non-hostile (or better depending on status damage); does not end naturally.
cold - 0.05% of status damage as HP damage per second; has a chance to inflict fear every second
fractured - 2% of status damage as penalty to stats
curse - 0.3% of status damage as MP damage per second; skills with MP cost can't be used.
fear - <as the name implies>
freeze - encased in solid ice: can't move, has a chance to inflict suffocation or panic every second
panic - <as the name implies>
poison - 0.2% of status damage as HP damage per second; also reduces all stats by 1% of status damage
stun - 90% reduced mobility for 5s
suffocate - <as the name implies>, can't be applied if the target does not need to breath
wet - 15% of status damage is added to the relevant attack stat of received ice or lightning attacks (at most doubles the stat), lasts 30s

Instant death is NOT available.
Effects that deal x damage per second deal damage in multiples of 0.1 and get rounded up to 0.1 if below.

Will add more as needed.

Exp is awarded for dealing damage relative to the fraction of damage dealt, overkill damage does not count.
E.g. a monster is worth 10 exp and sitting at 15/50 HP, if 20 damage is dealt to it 3 exp are rewarded.

Indirect means like status effects and environmental damage do count as well.
Only monsters are always worth exp, people only count if the system declares them "outlaws".

Non-combat experience can be earned by practicing, learning, cooking, cleaning, etc.
While tired/exhausted they grant no exp.

Low difficulty tasks/low effort exercises are worth 1~2 exp per hour, more effort and actually learning something can reach up to 10 exp per hour.

Before age 12 exp gain is reduced to 10% of the usual value for all exp sources.

In a party, exp is evenly split except that the one triggering the exp gain counts double, e.g. member A kills a wolf worth 20 exp while in a party with B and C then A gets 10 exp and B&C each get 5.

Exp cost to reach the next level increases by 15% of the previous value + 50x target level.

Exp is first put into a pool and then only applied once you rest.

How gained exp is split between classes, race, titles and extra can be configured in the settings, the default is an even split across all. MC chooses manual distribution.
Exp fractions are added but not visible on the status screen.

All titles share one level.

Alternatively to using exp you can rise a job class (but not other level types) for free by getting trained for 1 week by someone who has that same class. At most, you can get trained up to 1/4th of the trainer’s level in that class.

Total exp value of a monster is:
((HP/5 + MP/10 + SP/10 + sum of other stats) / 700) x (100% + level%)
keep fractions intact

Being born gives you a random class and a race-derived from your parents.
If a parent has multiple race classes you inherit a random one.
If both parents give a subrace the same main race (e.g. high elf and wood elf are both elves) you keep only one of the two.

To prevent certain subraces from going extinct there's a 5% chance that an inherited subrace mutates into a different subrace of the same main race, e.g. high elf and wood elf can make a dark elf child.

Races are capped at 2; hybrid children already have 1 race from each of their parents (e.g. classic half-elf has both human and elf).
Most races have variants/sub-races which they can add if they undergo a specific ritual.

Each race has at least one type weakness so having a variant is not a free power boost.

There are "extra" races like vampires that "modify" the base do not count for the cap and can't be standalone.

Acquiring an extra race after birth typically warps or overwrites the original personality (unless a skill explicitly prevents that).

For the sake of calculating stats your first class and base race count as having 20 levels more.
Hybrid races (e.g. classical half-elf) only gain 5 levels worth of bonus stats but in both the races.

Example stats:
Warrior gives 9 STR, Cleric 6 STR, Human 2 STR
Warrior(10), Cleric(5), Human(8) would have: (20+10)x9 + 5x6 + (20+8)x2 = 356 STR
Cleric(5), Warrior(10), Human(8) would have: (20+5)x6 + 10x9 + (20+8)x2 = 296 STR

Normally stat gains per class are capped at 9 or 60 for resource stats.
Needed to keep "glitch classes" in check.

Unlocking a class requires a certain amount of stats; this amount increases the more classes you already have.
Having someone train you who has the exact same class reduces this amount by 30%.

Base classes just require meeting the stat requirement, and for combat classes having a class core.
Elite classes additionally require having a thematically fitting base class (e.g. gunner, ranger or scout for sniper) at level 5 or above.

The base requirements for each stat are (target class's stat) x 10 x (2 + number of already unlocked classes) x (90% + 10% x number of already unlocked classes)

E.g. unlocking Warrior as a 3rd class requires STR: 9 x 10 x 4 x 110% = 396

A person is capped at 10 job classes; when an 11th class is forced one other must be deleted.
Otherwise, classes can't be removed, once a class is acquired it stays.

You can only have 3 elite job classes or up to 5 with the elitist title.

While selecting a class you can only see the stat growth and the skills which you can immediately use; normally you start a class at Lv1 so you only see the first skill, but e.g. summoned spirits may start higher based on the creator's stats so may show all skills.

There's a category of classes that count as a base class but require the royalty title, e.g. prince(ss)

Some "special" job classes exist that can't be taken naturally; e.g. failed hero.

Additionally, there exists a group of "divine" classes; these do not count towards the cap and you can only have one.

This category is basically reserved for heroes, demon lords, gods and cheat reincarnators.

Titles are capped at 20, deletion is not possible.

For each title beyond the first 5 exp required to the next title level increases by 10%.

A handful of titles can overwrite a different title, e.g. royalty replaces nobility.

Some titles are mutually exclusive, can't have "brave one" and "coward" at the same time.

A typical person earns about 20 low impact titles in their lifetime.

Base and elite classes can be acquired by meeting the requirements.

Cursed classes are forcefully gained through hostile actions (e.g. animate dead -> zombie).

Any monster class comes with the [mindless monster] skill which deletes their free will.

Titles are unlocked but dormant when you meet their requirements, e.g. Opportunist requires landing 10000 critical hits.

Some titles are limited and can be held only by a limited amount of people at the same time, e.g. there can only be one hero per world and up to six hero companions.

Dormant titles can be put as active, however, once a title is active this can't be undone.

Some titles are "forced", e.g. when you insult the gods and gain Fate Breaker, those skip the dormant step and go directly to active.

Only active titles give their benefits and count for title exp requirement adjustment.

Real world time is stopped during the dungeon crawl.
You can only enter one dungeon per week.

When entering a dungeon MP and SP are refilled, HP stays where it is.
While in a dungeon the effects of sleep are negated.

When you enter a dungeon the full set of monsters spawns, no further monsters spawn outside of specific mechanics/puzzles - puzzle related monsters always give 0 exp though.