Damage types
Physical damage types: blunt, slash, pierce. Elemental: fire, frost, lightning, poison, spirit. Chop and pickaxe are separate and only work on trees and rock respectively.
Every creature has its own resistance table: normal, weak, very weak, resistant, very resistant, immune. Weakness multiplies damage, resistance reduces it, immunity zeroes it. That is why choosing a weapon for the target matters more than raw numbers.
Poison and fire deal damage over time, and spirit hits the undead especially hard.
Armor reduces incoming damage non-linearly: against weak hits it almost zeroes the damage, against strong ones it cuts a percentage. So an advantage of one stage of armor feels stronger than the number suggests.
Blocking and parrying
A shield (or, without one, your weapon) has a block power, which the Blocking skill raises. Blocking reduces incoming damage but does not cancel it entirely. Regular blocking consumes stamina, while a successful parry costs none under vanilla settings. If stamina runs out or the damage absorbed exceeds your stagger limit, the hit goes through unreduced.
A parry is a block at the very moment of the hit. It multiplies the block power and knocks the enemy off balance, after which it takes increased damage. It is the main way to fight strong creatures without heavy armor.
Every shield has its own parry multiplier, and tower shields do not parry at all but hold strong hits. Blocking costs stamina; if there is not enough, you are knocked back.
Stagger
Every creature has a stagger threshold. When the damage accumulated in a short time exceeds it, the creature staggers and cannot attack for a while, and the damage it takes increases.
Stagger builds from blunt, slash, pierce and lightning damage equally; some attacks build it faster: sledgehammers ×2, battleaxes ×1.5, some secondary attacks far more. A well-timed parry staggers the attacker if it can be staggered.
Backstab
If you hit a creature that has not noticed you, the damage is multiplied by the backstab coefficient. Knives have the highest one, most weapons have triple.
The multiplier only works while the creature has not noticed you, so knives rely on the first strike and bows on a shot from afar.
On the weapon card the coefficient is shown in the “Backstab” line.
Sneaking
Visibility depends on lighting, movement and the Sneak skill. Some armor, such as the set made of troll hide, makes you quieter.
Sneaking costs stamina while you move crouched; standing still while crouched does not drain it. The skill reduces both the cost and the distance from which you are noticed.
Creatures hear and see separately: running in the dark will still give you away by sound.
Factions
Creatures belong to factions. Members of the same faction do not attack each other (a troll and greydwarfs share one), while different factions are mostly hostile, with exceptions: the Dvergr are neutral toward the player until one of them is hit.
Tamed animals belong to the player’s faction and defend the base.