Formulas

All results are floored (rounded down to nearest INT). Many formulas have been Datamined long time ago and as such should be taken with a grain of salt (the game is currently much harder to datamine)

HP = VIT * 4.7 + LVL * 7.4
PATK = STR * 2.1 + LVL * 5.6 + 50
MATK = MAG * 2.1 + LVL * 5.6 + 50
PDEF = VIT * 1.1 + STR * 0.5 + LVL * 5.6 + 50
MDEF = VIT * 1.1 + MAG * 0.5 + LVL * 5.6 + 50

DAMAGE FORMULA = (ATK * 1 - DEF * 0.5) * 0.4  * (SKILL POWER * (1 + % SKILL DAMAGE MODIFIERS FROM SKILL LEVELS) / 100) * (1 + % DAMAGE MODIFIERS) * (1 + TARUNDA/TARUKAJA - RAKUNDA/RAKUKAJA) * (CHARGE / CONCENTRATE: 2.25 or 2.75 w/ Templar Dragon) * (CRIT/WEAKNESS/RESIST)
10% variance in final damage. 
Critical hit multiplier is 1.5x
Weakness hit multiplier is 1.5x
Resistance hit multiplier is 0.7x

HEALING FORMULA = (MATK * (HEAL POWER * (1 + % HEALING MODIFIERS FROM SKILL LEVELS) / 100) * HEALING_CONST + MIN_HEAL_VAL) * RANDOM_HEA_VAR * (1 + % HEAL MODIFIERS)

-kaja/-kunda effects (applied at end of formula) 
Rakukaja: -0.17 = 0.83x damage taken
Tarunda: -0.2 = 0.8x damage taken
Rakukaja + Tarunda: -0.37 = 0.64x damage taken
Tarukaja: +1.2 = 1.2x damage dealt
Rakunda: +1.25 =  1.25x damage dealt
Tarukaja + Rakunda: 1.45 = 1.45x damage dealt

STATUS CHANCE = BASE STATUS CHANCE + BRAND STATUS CHANCE + STATUS CHANCE PASSIVES - ENEMY STATUS RESIST + (USER LUCK - ENEMY LUCK) * 0.5
MINIMUM STATUS CHANCE = SKILL_ADD_RATE * UNKNOWN CONSTANT
It will take the higher result of the two formulas above.

TEMP ACCURACY = BASE SKILL ACCURACY * (FUNCTION1(USER AGI - ENEMY AGI) + FUNCTION2(USER LUCK - ENEMY LUCK)) * (1 * SUKUNDA/SUKUKAJA)
FINAL ACCURACY = TEMP ACCURACY + ACC BRANDS + ACC SKILLS - EVASION BRANDS - EVASION SKILLS 
There is a minimum hit chance, and it will take either that or the accuracy depending on what's higher.

LUCK DIFF = USER LUCK - ENEMY LUCK
CRIT LUK VALUE = 20 if LUCK DIFF >= 30, 
                 15 if LUCK DIFF >= 20, 
                 10 if LUCK DIFF >= 10,
                 0 if LUCK DIFF >= 0,
                 -10 if LUCK DIFF >= -256
CRIT CHANCE = CRIT LUK VALUE + BASE SKILL CRIT CHANCE + PASSIVE SKILLS/PANEL CRIT CHANCE + CRIT BRANDS - ENEMY CRIT REDUC SKILLS/PANEL + Dx2 CRIT SKILL
Crit chance is clamped to lie between 0 and 100 inclusive.
BASE SKILL CRIT chance seems to be 10 on phys skills which don’t list their crit rate in their description*

Counter Chance is rolled sequentially and separately, starting from the highest tier Counter first (Death Counter>Retaliate>Counter) regardless of slot order.

Party speed is calculated first at an individual demon level then at a party level.
INDIVIDUAL DEMON SPEED = (DEMON AGILITY + SKILL AGILITY + MITAMA AGILITY) * ((SKILL SPEED PERCENT + BRAND SPEED PERCENT + PANEL PERCENT) / 100)
PARTY SPEED TOTAL = INDIVIDUAL DEMON SPEED TOTAL / PARTY COUNT (It's an average)