Main Damage Types
Damage can be classified as:
Special Damage Mechanics
Hyper Mode
Attack power boosted when HP is low by equipping certain items. Red Tearstone ring and Morion Blade both activate hypermode and the effect stacks for both items including an additional Morion Blade (but not another Red Tearstone Ring).
Counter Damage
Counter hits occur when one is attacked mid-attack animation, dealing additional counter damage. This is due to the counter state, wherein one's absorption VS damage is temporarily reduced during an offensive action such as attacking or kicking, making them more vulnerable against damage.
Only Thrust damage can deal Counter Damage, which can be further boosted with the Leo Ring.
Standard Arrows, Standard Bolts and Dragonslayer Greatarrows gain an additional 10% bonus Counter Damage compared to other ammunition.
Instability Damage
Instability damage is triggered when one is hit during a few specific animations. A special "thunk" sound will play to indicate the difference from a normal counter hit.
Valid animations: within certain frames in normal attacks, parried, guard-broken, poise-broken (certain bosses and enemies), during jumping attacks, recoiling after striking a solid object, changing direction suddenly when dashing, recovering after dropping from sufficiently high altitude.
Critical Damage
Critical damage can be dealt by either riposting or backstabbing an enemy. A riposte can be done through parrying; guard breaking; or attacking after having dealt a sufficient amount of damage to a few select, non-player enemies' heads (the last form of riposte often referred to as a "visceral attack").
The weapon's Critical modifier will be applied to the weapon's damage during any of these attacks, increasing damage dealt.
Critical attacks with Dark damage is reduced against other players (but still functions normally for mobs.)
The Assassin's Mark, Elden Ring and Hornet Ring can be used to increase the damage dealth with critical attacks.
The Footman's Overcoat and Ironclad Armor can be used to null the damage of backstabs.
The Rare Ring of Humanity prevents against any form of critical or grab attacks.
Headshot
If an enemy is shot in the head by an enemy projectile (i.e. with a bow/crossbow), its poise will be broken and will be temporarily stunned.
The damage applied is also increased by 50%. This also applies to many humanoid enemies with little or no protection on their head.
The scythe skill Neck Swipe also counts as a headshot.
Headshot damage can be prevented by using the Iron Keeper Helm.
Falling Damage
Falling is gravity calling your name for either a safe fall, a proportionate amount of damage, or death.
Fall damage in Cinders has been changed to make non-lethal falls always survivable as long as the current Equipment Load is below 70% and HP is fully replenished. These same falls can also be survived with higher equipment loads or less than 100% HP as long as enough Vitality is leveled up. Inversely, the closer equipment load is to 0%, the less damage will be taken from any survivable height.
Boots of the Explorer, Jester's Tights, Pickpocket Leggings, Spook and the Silvercat Ring will completely negate all fall damage as long as the fall is not otherwise lethal for you.
The Malus of the Ordained increases all damage received from falling by 500%.
Example: Fall down off the cliff next to Eygon Of Carim (Irina Of Carim's watcher in Undead Settlement) and you'll live with a sliver of health at max health. Fall down much farther than that with falling damage protection on, and you'll automatically die.
Information here is accurate for version 2.15.