Accuracy, avoid and critical hits

A hit's damage roll is only the start: the monster may evade it, the hit may miss, and a lucky roll doubles it. The same kind of checks decide whether a monster's touch hurts the hero, and how much.

Evade, miss and critical hits

Each hit of the hero passes three checks, in this order.

The monster evades with a chance in percent of the monster's level minus the hero's ACC. The monster shows MISS. The hit still counts as having reached a target, so it is used up: a star stops and a piercing attack loses one of its targets. A hero whose ACC is at least the monster's level is never evaded.
The hit misses if its damage is below 1, or with a chance in percent of half the monster's level minus the damage. MISS shows and nothing else happens. Once the damage reaches half the monster's level, a hit never misses.
A critical hit comes with a chance of the hero's critical rate in percent. It doubles the damage, and the phone vibrates.

Then the monster loses the HP.

A chance of 0% or less never succeeds and one of 100% or more always does.

Example (made-up numbers): a level 30 monster, a hero with 22 ACC, a 9-damage hit and an 8% critical rate. The monster evades 30 minus 22 = 8% of the time; the hit misses 30 / 2 minus 9 = 6% of the time; 8% of the hits that land are critical, for 18 damage.

Monster damage and the hero's avoid

A monster hurts the hero by touching. Each tick, the game checks every monster whose box touches the hero's:

While Dark Sight is on, contact does nothing.
A Malady Bomb that touches the hero explodes: it dies and deals its damage roll.
Otherwise the hero first tries to avoid it, with a chance of (the hero's AVOID minus the monster's level) × 4 in percent. An avoided touch deals 0 and shows MISS.
If not avoided, the hero takes the monster's damage roll.

The damage roll. L is the monster's level and D the hero's DEF.

d = L × L / 30 + 2 × L + 20, minus D × 7 / 3.
If d is below 0, the roll is from 1 to L / 2.
Otherwise the roll is d plus a number from minus (2 + d / 4) to d / 4 + 2.
The damage is the roll × 90 / 100.

A high DEF therefore never makes a touch harmless: the damage only falls to between 0 and about 0.45 L.

Bosses' attacks. A boss's skill attack deals twice the damage roll and cannot be avoided. Each attack hits at most once.

Hazard maps. In the Abandoned Mine (area 10; the rule also names an area 11, which no shipped map has), the hero takes 300 damage every 50 world ticks (2.5 seconds), unless wearing Fire Suit.

Example (made-up numbers): a level 20 monster against 15 DEF. d = 400 / 30 + 40 + 20 minus 105 / 3 = 13 + 40 + 20 minus 35 = 38. The roll is 38 plus minus 11 to 11, so 27 to 49, and the damage is 24 to 44. A hero with 24 AVOID avoids the touch (24 minus 20) × 4 = 16% of the time.

Taking damage

The hero. With Meso Guard on, the skill tries to pay meso for the blow: (damage / 2) × the skill's value / 100 meso. If the hero has that much, the damage is halved. HP then drops by the damage, and at 0 the hero dies. Unless on a ladder, the hero is knocked back, away from the hit at 1.5 times the jump's sideways speed and up at half the jump's push. A short invulnerability follows; an avoided touch starts a shorter one.

A monster. After the three checks above:

Drain heals the hero by the damage × the skill's value / 100, up to the maximum HP.
With Pickpocket on, the hit drops meso with a chance of the skill's value in percent: an amount from the monster's meso / 18 minus 5 to its meso / 18, which then goes through the usual 80% meso roll (drops).
HP drops by the damage. At 0 or below the monster dies; otherwise a normal monster is knocked back for a short while and shows its HP bar.

Example (made-up numbers): Meso Guard with a value of 80 and a blow of 40 damage. The guard costs 20 × 80 / 100 = 16 meso; a hero with 16 meso or more takes 20 damage instead of 40.

Sources

CMob::RollEvade 0x72639 (from the attack objects 0x766F1 and 0x76AED), CMob::TakeHit 0x73715 (miss, damage, Drain, Pickpocket), CHero::RollCritical 0x6039D, CHero::CheckMobContact 0x65F05, CHero::RollAvoid 0x603DD, CMob::RollDamage 0x6F591, boss attacks 0x6EF6D checked by CHero::CheckAttackHit 0x65DC5, CHero::TakeDamage 0x65B55, CSkill::MesoGuard 0x7EAB1, CSkill::Drain 0x7D4A5, CSkill::Pickpocket 0x7EB35. The chance functions are Rand_Percent 0x226B9 and Rand_Range 0x22641. The real-asset test play.mechanics checked the hero's hits and the monsters' contact damage of a 60-kill hunt against these rules.