Mechanics

Rally Effect
When you get hit, a mechanic called the Rally Effect kicks in which allows you to regain some of the health you lost by damaging enemies.

Upon taking damage, health is initially reduced as normal, and the portion of the health bar removed by the hit turns from green to orange, indicating the current health value which can be reached by dealing damage. This orange portion of the bar, by default, begins to shrink after an 0.08-second delay at a rate of 30% of maximum health per second until it disappears entirely, leaving only the green portion and indicating that the Rally Effect has ended. If the player takes damage a second time while an orange portion of the bar remains, it is discarded completely, and a new orange bar appears based on the new health lost, resetting the Rally Effect.

While an orange portion of the health bar remains, damaging enemies heals the player for 12% of damage inflicted with an upper limit of 20% of the original health lost per instance of damage dealt. Health recovery in this manner is reduced by 65% while the player is being protected by a force field (such as the ones granted upon taking hits with a Shield equipped).

Sudden Death Prevention
If the player takes a hit that would normally kill them while their health is above 25% of maximum health, that hit instead reduces health to 1. If this mechanic triggers, all nearby enemies will be stunned for about one second. This mechanic takes 45 seconds to recharge before it can be triggered again.

Weapon Stats-Damage Multiplier and Damage Reduction
Gear items with a sufficiently high gear level will begin to exhibit special effects which scale with gear level:
 * Weapons and skills that deal significant damage, whether directly or indirectly, gain +25% damage multiplier for every 2 gear levels above gear level 1 (I), including bonus gear levels added by "+", "++", "S", or "L" variants. Damage multiplier is a local effect which increases the base damage dealt by the item on which it is found (before it is scaled up to its final value by Stats). It is automatically rolled into displayed damage output due to being applied unconditionally (i.e. it is not a situational damage multiplier like most damage-increasing Affixes).
 * Weapons and skills which do not deal significant damage on their own, usually possessing the No Damage or Negligible Damage tag, instead gain -5% damage taken for every 2 gear levels above gear level 1 (I). Reductions to damage taken from gear levels, called damage reduction, are global effects which stack additively to each other, up to a limit of -75% damage taken.
 * All amulets start with -10% damage taken at gear level 1 (I) and gain another -10% damage taken for every 4(?) gear levels above gear level 1 (I). Damage reduction from amulets stacks with damage reduction from weapons and skills up to the aforementioned cap.
 * Note: the damage reduction cap of -75% damage taken only applies to the bonuses given by gear levels. Reductions to damage taken from other sources, such as Shields and damage-reducing Affixes, apply separately.

Breach
If the player deals a significant amount of damage to an enemy within a short amount of time while they are in the middle of an attack or defensive maneuver, the overwhelming force may breach that enemy's defenses, interrupting the maneuver and stunning them for 1.4 seconds.

Basic Mechanics
By default, damage dealt to enemies by direct hits (not by damage-over-time effects) increments breach damage by the amount of damage inflicted. Breach damage, for an enemy with an enemy tier of 1, decays at a rate of 20 points per second until it reaches a value of 0, and breach damage must exceed 100 points in order to cause a breach to occur. Breach damage decay rate and required breach damage to cause a breach both scale with enemy tier using the same scaling formula used to increment enemy health.

Breach Resistance
Enemies can be more or less resistant to being breached during certain maneuvers. The degree of resistance or vulnerability is quantified by the maneuver's breach resistance as follows: In general, larger enemies are harder to breach than smaller enemies, melee attacks have higher breach resistance than ranged attacks, and Bosses and their minions are immune to being breached.
 * If a maneuver's breach resistance is equal to 0, breach damage accumulates normally as the enemy takes damage during the maneuver.
 * If a maneuver's breach resistance is positive (greater than 0), damage taken by the enemy during the maneuver is reduced by (breach resistance x 100)% for the purposes of breach damage accumulation (e.g. if a maneuver has a breach resistance of 0.5, a 40-damage attack would only increase breach damage by 20 points).
 * If a maneuver's breach resistance is equal to 1, the enemy cannot be breached at all during the maneuver due to damage taken being reduced to 0 for the purposes of breach damage accumulation.
 * If a maneuver's breach resistance is negative (less than 0), damage taken by the enemy during the maneuver is increased by (-(breach resistance) x 100)% for the purposes of breach damage accumulation (e.g. if a maneuver has a breach resistance of -1.5, a 40-damage attack would increase breach damage by 100 points, enough to cause a breach to occur if the enemy has an enemy tier of 1).

Breach Bonus
Some of the attacks from the player's Weapons are more or less effective at causing breach damage on all enemies. The degree of effectiveness of breach damage generation for a particular attack is quantified by its breach bonus as follows :
 * If an attack's breach bonus is equal to 0, breach damage is equal to attack damage.
 * Damage from Shields and non-Weapon sources can be assumed to have a breach bonus of 0.
 * If an attack's breach bonus is positive (greater than 0), breach damage is increased by (breach bonus x 100)% compared to breach damage for a breach bonus of 0 (e.g. if an attack with a breach bonus of 1 deals 40 damage, that attack increases breach damage by 80).

In general, breach bonus is higher for melee attacks than for ranged attacks, greater for final blows of weapon combos than for first blows, and larger for slow weapons than for quick weapons.
 * If an attack's breach bonus is negative (less than 0), breach damage is decreased by (-(breach bonus) x 100)% compared to breach damage for a breach bonus of 0 (e.g. if an attack with a breach bonus of -0.5 deals 40 damage, that attack increases breach damage by only 20).
 * If an attack's breach bonus is equal to -1, the attack cannot cause a breach to occur due to damage being reduced to 0 for the purposes of breach damage generation.

Note: The bullet points for breach bonus effects assumed that attacks were occurring during enemy maneuvers with a breach resistance of 0. For cases in which breach bonus and breach resistance are both non-zero, final breach damage is obtained by applying the attack's breach bonus effect first, then the enemy maneuver's breach resistance effect.

Dive Attack
When falling from any distance, by pressing the jump and down button at the same time, a dive attack can be performed. This attack negates the stun from falling down long distances and deals damage to enemies. Stun will, however, still be applied if the dive attack is long enough (e.g. the height of the exit elevator in Ramparts).

Three levels of damage can be dealt with the dive attack. If the distance fallen is at most that achieved by double-jumping from a flat region with no platforms or ledges nearby, the player deals 35 base damage in a 1-tile radius (60 base damage in a 2-tile radius if the player possesses the Belier's Rune). If the distance fallen is more than double-jump height, the player deals 90 base damage in a 2-tile radius (110 base damage in a 4-tile radius if the player possesses the Belier's Rune). If the distance fallen is more than 2.5 stories, dive attack damage is increased by a further 50%, producing final base damage values of 135 (without Belier's Rune) and 165 (with Belier's Rune).

Dive-attacks scale their damage based on the damage bonus granted by the highest of the player's stats. As damage to enemies comes from a vertical direction, dive attacks do not trigger the thorns effect of Thornies.

Shield Force Field
Having a shield in inventory causes a force field to manifest around you for 0.5 seconds when you take damage, protecting you from getting damaged further for the duration.

Accelerated Movement
By killing 8(?) enemies in a short amount of time, you gain a movement speed buff which initially lasts for 7 seconds by default (21 seconds with the Velocity Mutation) and grants boosts to running, rolling and climbing speeds. Killing enemies while affected by this buff refreshes its duration.

Falling
Unless you fall off of a building in The Ramparts (in which case you take 30 base damage, scaled by the monster level of the zone), there is no fall damage in Dead Cells. However, if you fall from a long enough distance, you will be temporarily stunned. The stun lasts longer if you have fallen more. Enemies, however, can get hurt and killed from a fall. This distance is much shorter than the distance that will cause the player to be stunned, so using something that causes knockback such as the Assault Shield or the Spartan Sandals to take advantage of this is a good idea.

Dive attacks prevent the stun caused by falling. However, there is also a limit of how much the dive attack can prevent this stun. Really high heights, such as one found in some safe areas past The Collector, can still cause a falling stun even if the player dive attacks. Rolling in mid air will reset the dive, allowing you to dive again during very long falls.

Parry
Shields can be used to parry attacks, nullifying their damage entirely rather than merely reducing it, and briefly stunning the attacker. Parry can also reflect most projectiles.

More information on this mechanic is given on the Shields page.

Status Effects
There are six status effects: Stun, Freeze, Immobilize, Poison, Bleed, and Burn. These fit into two broad groups: preventing enemy action (Stun, Freeze, Immobilize), or dealing damage over time (Poison, Bleed, Burn). Additionally, Weapons and Skills can have modifiers that increase damage dealt to an enemy suffering from a specific status effect (though no modifier increases damage against immobilized enemies).

Stun
Stun incapacitates a target for the Stun's full duration, regardless of what happens to it in that time. Stun is a good time to kick some ass. You can also be Stunned, especially by Falling, and enemies with a shield.

Freeze
Freeze is like Stun, lasting longer but ending when damage is taken. Freezing is good for managing groups of enemies or repositioning, but it won't really let you deliver a beatdown. Note that a weapon that both Freeze and a DoT (ex, Burning) will break the Freeze with the first tick of the DoT.

Immobilize
Immobilize prevents an enemy from moving or turning, though it can still perform actions and attack. The most important thing about immobilize is that it stops enemies from even turning around. Because most enemies cannot attack you while facing away from you, they might as well be stunned while you're behind them.

Poison, Bleeding, Burning
Poison, Bleeding, and Burning all do damage over time. They can be stacked with each other or with themselves to increase the damage. The only real differences between them are their sources. Note that all of them will break Freeze with the first tick of damage.

Environmental Effects
Certain items with elemental effects can interact with each other and the environment to the benefit (or detriment) of the player:

Oil-Fire Interactions

 * Enemies which are affected by stacks of oil take 8% more damage from burning effects for each stack present.
 * Creating pools of fire on oil slicks (or vice versa) causes the slicks to ignite, producing blue flames which deal the expected burning damage but last for longer than normal red flames (ignited slicks burn for the duration of the slick while pools of fire outside of slicks burn for a much shorter duration).
 * Oil explosions, whenever they occur, deal 16 base damage.

Liquid Interactions

 * Enemies in pools of liquid are immune to burning effects.
 * Enemies that take damage from ice-element attacks while standing in a pool of liquid cause the pool to chill dramatically, causing all other enemies in the pool to be slowed as if they had recently thawed after being frozen.
 * Enemies that take damage from electric-element attacks while standing in a pool of liquid cause the pool to become electrified, dealing 18 base DPS to all enemies in the pool for 2 seconds. Shock DPS scales with the scaling stat of the item producing the attack that electrified the pool.

Infection

 * Taking damage from Key Elite in The Castle causes infection.
 * Maximum tier of infection is 10.
 * Key Elites' hits gives you 2 points of infection.
 * After reaching maximum infection tier, you start taking enormous damage, then you just die.
 * This effect can occur from Prisoners' Cells if 4 Boss Source Cells are inoculated (currently exclusive to the Baguette Update alpha.).
 * In that case, every enemy can foment infection.