Block

Attributes
HP	ATK	DEF	RES	Attack interval	Cost
Rdpl. time	Block	Movement speed	Weight	E-RES	ERST

Block represents how many enemies that can be blocked by the unit. Melee Operators (as well as ranged ones in certain situations) and certain deployable and static devices can block enemies once they are on the same tile as each other, halting the enemy's advance as they are forced to stop and attack the blocking unit. However, if the amount of enemies on the same tile as the friendly exceeds their block count, the additional enemies will move past the friendly.

Blocked enemies are treated as being within the blocking unit's range, regardless of whether that is the case or not. If the enemy is invulnerable while being blocked (e.g. when put to Sleep or are transitioning into the next phase for most bosses) they will use the usual hitbox mechanic to determine whether or not they are within the range of the blocking unit, which can be detrimental for units that can attack sleeping enemies if the victims are being blocked while behind them.

Unblockable

The following enemies cannot be blocked.

Innate

Normal
Elite
Boss

• All Waregeists' true forms

Ability

Enemy	Information
	The High Priest cannot be blocked.
	Becomes unblockable while their respective Holographic Mirage (MK2) is present.
	Becomes unblockable while over Nethersea Brands.
	Cannot be blocked in the first phase.
	Becomes unblockable when charging.
	Stitch cannot be blocked.
	Becomes unblockable once their identity is confirmed.
	Cannot be blocked while on the Self-Destruction state.

Multiple block

The following enemies are counted as more than one unit when blocked, thus they can only be blocked by units whose available block count are equal to or higher than how much block count the enemy takes up.

2 units

Elite
Boss

3 units

Elite
Boss

4 units

Elite

Variable

Enemy	Information
	Normally counted as one enemy when blocked; when their HP falls below 50%, the Brandguider will be counted as two enemies instead.
	From its second phase, the Endspeaker is counted as three enemies when blocked. If the Endspeaker had Consumed the Remains of a Regressed Brandguider in the previous phase, it will be counted as four enemies when its HP falls below 40%.
	Normally counted as one enemy when blocked; each Star Ring on the map increases Kristen's block count requirement by 1.

Interactions

Friendly

• Certain friendly units, notably Centurion and Crusher Guards, are capable of hitting multiple targets equal to their block count in each attack, through their trait, talent, or skill.
  • Most of the time, the game erroneously states that said units are able to "attack all blocked enemies"; the unit does not actually have to block the enemies to attack them.
  • Should the above units' block count is somehow reduced to 0 (see below), their attacks will hit one target at a time as with other units.
• Reaper Guards' HP recovery in each hit is capped to their block count of one or two from Elite 1.
• Stunned friendly units cannot block enemies at all, even if their block count is somehow increased by external sources. This quirk also applies to the following:
  • Standard Bearer Vanguards while their skill is active
  • Liberator Guards while their skill is inactive
  • Flint while Display of Might is active
  • Kafka while her skill is active due to Misdirection
  • Dollkeeper Specialists' Substitute
  • Ashlock while Focused Bombardment is active
• While friendly units block enemies, the invisibility of both will be disabled, unless if the blocking unit is in a Bush or Exhaust Grille.
• While not blocking enemies:
  • Lord Guards use a ranged attack which deals 0.8× damage.
  • Fortress Defenders use a ranged AoE attack.
• Instructor Guards has their ATK increased to 1.2× when attacking enemies that they are not blocking, which further increases to 1.3× with their respective INS-X Operator Modules.
• Artilleryman Snipers and Dreadnought Guards with their respective ART-X and DRE-X Modules, respectively, have their ATK increased to 1.1×/1.15× when attacking enemies that are being blocked, even if they are not blocked by the Artilleryman/Dreadnought themselves.
• Duelist Defenders can only restore/recover SP while blocking enemies.
  • With their respective HES-X Module, the Duelist restores/recovers SP at a mere 20% of the normal rate while not blocking enemies instead.
  • With their respective HES-Y Module, the Duelist can restore SP while not blocking enemies.

Operator	Subject	Interaction
	Sharp Nails	Enemies attacked by Aosta will bleed for 3 seconds so long as they are not being blocked, during which they take Arts damage equal to a portion of Aosta's ATK every second. The bleed damage is doubled while Shadow Nails is active. Elite 1: 12% Elite 2: 18% Potential 5: +2%
	Activate Phase Blades	Enemies blocked by friendly units in the surrounding tiles to Ayerscarpe will be struck by a melee attack that deals Arts damage equal to a portion of Ayerscarpe's ATK whenever he attacks. Level 1: 70% Level 2: 80% Level 3: 90% Level 4: 100% Level 5: 110% Level 6: 120% Level 7: 130% Spec. 1: 140% Spec. 2: 150% Spec. 3: 170%
	Protean	Increases ATK when blocking enemies or ASPD otherwise. Elite 1: 6%/6 Elite 2: 12%/12 Potential 5: +2%/+2
	"Really Cold Axe"	The attack with "Really Cold Axe" target enemies who are not being blocked over the others.
	Ally Support	Fartooth can attack blocked enemies outside her attack range.
	Featherweight	Increases the damage dealt when Flint attacks enemies she aren't blocking. Elite 1: 20% Elite 2: 40% Potential 5: +5%
	Battleaxe	Each enemy blocked by Gavial the Invincible further increases the ATK and DEF buff, which can stack without a limit. Elite 1: 3% Elite 2: 4% Potential 3: +1%
	A Disastrous Drowning	Harmonie will only attack blocked enemies.
	Unexpected Arrive	Increases the damage dealt when attacking blocked enemies. Elite 1: 12% Elite 2: 17% MSC-X Stage 2: 20% MSC-X Stage 3: 22% Potential 5: +3%
	Pain Focus	Reduces Physical and Arts damage taken from enemies not blocked by Lessing while he is blocking enemies. Elite 1: 20% Elite 2: 35% The damage reduction is increased to 2× (2.2× at Spec. 3) while Clash of the Faithful is active.
	Oathbreaker	Increases the Physical damage dealt when attacking blocked enemies. Level 1: 145% Level 2: 145% Level 3: 150% Level 4: 160% Level 5: 165% Level 6: 170% Level 7: 180% Spec. 1: 190% Spec. 2: 200% Spec. 3: 220%
	Blazing Sun's Obeisance	The Radiant Knight will deal True damage when attacking enemies being blocked by herself or Blazing Sun.
	"As You Wish"	Rosmontis will only attack blocked enemies.
	Rosmontis's Tactical Equipment	Enemies blocked by the Tactical Equipment have their DEF reduced by 160.
	Vulnerability Deconstruction	Amplifies the Physical damage taken by blocked enemies while Sesa is deployed. Elite 1: 7% Elite 2: 15% Potential 5: +2%
	Arts Sniper	Amplifies the Arts damage taken by blocked enemies while Skyfire is deployed. Elite 1: 7% Elite 2: 15% Potential 5: +3%

Enemies

Certain enemies will use a melee attack when blocked or a ranged attack otherwise, which may have different properties depending on the enemy in question, but those are not listed here due to their numbers.

Enemy	Interaction
	Will "blink" past the friendly unit blocking her when blocked (15 seconds cooldown).
	Gains 40/50 RES while blocked.
	Tiacauh Warriors/Guards gain 130/180 DEF while blocked. Tiacauh Ritualists/Shamans gain 200/300 DEF while blocked.
	Their attacks reduce the target's block count by 1 for 5 (Agent)/10 (Agent Leader) seconds.
	Will erupt after being blocked for 10 seconds, dealing 1000/1800 (Level 1) Arts damage to friendly units in a radius of 1.4 tiles around Pompeii.
	While blocked, the Brave/Champion and the blocker have their DEF reduced by 70%, with the former can only be damaged by the latter and has an aggression level of -1.
	Their ability to deal Arts damage every second will be disabled while blocked.
	Can only be blocked by friendly units whose Hui/Ming attribute matches them.
	Will dash past the friendly unit blocking her when blocked and deals Physical damage equal to 150% of her ATK to friendlies she dashed through (immediately used when blocked the first time, 30 seconds cooldown).
	Can dodge Physical (and Arts for Ominous Apparitions) attacks 40% of the time while not blocked.
	Can dodge Physical and Arts attacks 40% of the time while not blocked. Will dash past the friendly unit blocking him when blocked and spawns an Ominous Apparition on his previous position (10/15 seconds cooldown).
	Will dash past the friendly unit blocking him when blocked (40 seconds cooldown).
	Takes 25% (50% in the second phase) less Physical and Arts damage from friendly units that are not blocking him.
	Takes 50% (75% for Alloy Surfing Instructors) less Physical and Arts damage while not blocked.
	Will devour the blocking friendly unit when blocked for the first time, instantly defeating the blocker and increases the Devourer/Maw's DEF by 700 but reduces their speed by 30%; if the devoured friendly was an Operator, they cannot be redeployed until the Devourer/Maw leaves the map.
	Takes 50% (35% in Round 2) less damage while not blocked.
	All Civilians and Spies whose identity is not confirmed/compromised yet will become unblockable unless if the Instigator/Agitator is blocked themselves.
	After landing three attacks when blocked, they will dash 1.5 tiles towards the next checkpoint on their path and deals Physical damage equal to their ATK towards the blocking friendly unit.
	Their attacks reduce the target's block count by 1 for 3 seconds. If the target is on a Gravity Switch, their block count will be reduced to 0 instead.
	One of the effects of his Demand reduces the block count of all friendly units at the time it is activated by 1, which increases to 2 on the second phase.
	Their speed buff upon taking damage will expire as soon as they are blocked.
	Its Speeding Mode will be forcibly ended after the Smiley collided with friendly units with a block count of at least 4 five times.

• Reborn Creations increase the block count of friendly units blocking them by 1, which can be increased to +6 this way. Since the Creations are still counted when blocked, this essentially means that up to 6 Reborn Creations are excluded from the friendly unit's block count.

Other

• The Londinium Secondary Defense Artillery will target the friendly unit with the highest block.
• "Supersweetie Superblends" increase the block count of friendly melee units by 1, which stacks without a limit but will be removed when the "Supersweetie Smiley" collides with the friendly on its Speeding Mode.

Advanced: Block Manipulation

Since Block mechanics tie with several other systems in Arknights, such as targeting, it is possible via skills and mechanics which alter block count to perform "block manipulation", i.e. change which enemies are or are not blocked, and by which operators. It is an extremely advanced mechanic that functionally only sees use in high level play. The most obvious example of block manipulation comes from Heidi, whose skills are entirely predicated on modifying the block count of friendly operators.