If a dummy of your unit cannot kill a dummy of the enemy target in one hit, an enemy with 3 dummies or more cannot be killed in one attack. 

Terminology#

Because all of my topics are hard and confusing enough I guess. 

It mostly also makes it easier for me to write things since I can say "hit" instead of "instance".

What is Link Protection and how does it work?#

Link protection is an important yet obscure mechanic that works into almost every attack received by any unit. The general idea is very simple. no hit (a single instance of damage) can overkill, unless if the attack ignores Link protection. 

As such, a hit deals unlimited damage but follows the rules of Link Protection can and will always kill only one dummy, even if that dummy has 1 hp, and the other dummies will be left at full health. 

Non-AOE Damage (Standard Attacks)#

A unit with 5 dummies will deal 5 hits when their attack lands. 

Take a unit with 5 dummies and 100 hp each. If an attacker with 5 dummies attacks with 80 damage, the unit will survive with 3 dummies with the top dummy having 20 hp. 

This is how it works out. 

Every hit from a regular attack is applied to the exposed dummy. When the exposed dummy only has 20 damage, the hit will only do 20 damage regardless of what number appears from the damage display. 

Remember the first line of this topic? This is why that is true.

This is more obvious from enemy attacks. Some bosses, notably Destroyer, do massive damage whenever they actually land a hit, but regardless of how much hp your tank has, they only lose one dummy from every attack. This effect does apply to your units when you attack enemies as well, but it is less obvious because you often need multiple attacks to kill an enemy, sometimes even needing multiple attacks for a single dummy link. 

Anyways, here's the formula. 

Final Damage = Min(Target exposed dummy HP, Hit Damage)

AOE Damage (Grenades/Airstrike/Others)#

AOE Damage follows slightly different rules. Take a unit with 5 dummies and 100 hp each. If a grenade with 80 damage lands on the unit, the enemy will be left with 1 dummy at 100 hp. 

However, this does not seem to make sense. The numbers are exactly the same as regular attacks, but why did Link Protection not work? And this is why I have prepared this handy table. 

The main reason is that grenade damage is applied to each enemy dummy, but enemy health is not represented for each dummy. Internally, the game represents the enemy HP as [Number of Dummy links] and [HP of exposed link]. Since the HP of each individual dummy is not represented, it is not possible for the unit to have multiple semi-damaged dummies without overhauling their entire system.

However, Link Protection does apply to grenades. 

If the enemy has 4 dummies with 100 hp each and 1 dummy with 20 HP, this is what a grenade with 80 damage will do. 

Since only one dummy can be damaged at a time, link protection only protects the top dummy.

This means that if a unit with more than 1 dummy is hit by a grenade whose damage is less than the max hp of its dummy, the grenade will not completely kill the unit. An unit with 2 dummies, with 100 and 1 HP respectively, will survive a 99 damage grenade with 1 hp. 

Anyways here's the formula if you want a less-tabley version.

Final Damage = Min(Target exposed dummy HP, AOE Damage) + Min(Target Dummy Max HP, AOE Damage)*(Number of dummies - 1)

Important Distinction: Dreamer beam is an attack with an area of effect, but deals non-AOE damage, as it only deals a single hit per tick (with a fast tick rate). And like Dreamer, not all attacks which hit dolls in an area deal AOE/Grenade damage.

Additional Notes#

Here are some other things that are related to link protection. 

1. Simulations

Simulations are usually done against a single enemy with 1 dummy. Because link protection and actual overkilling (where hits are wasted on a unit if the last dummy dies before all the hits are applied to the unit) happen so often in battles, your units will rarely do as well as your simulations. 

At the same time, simulations DO give you a general idea of who deals a lot of damage and who doesn't. This is an additional reason why you must take account of how the unit deals damage (few high damage attacks vs many low damage attacks) instead of slapping your strongest units in an echelon. 

2. Accuracy

An enemy with 5 dummies can survive a standard attack as long as it can dodge any one out of 5 hits, regardless of how much damage the attack does. With 60 ACC, a 15 EVA enemy has a 1 in 5 chance of dodging every hit, meaning that on average you will always need 2 attacks to kill the enemy despite doing infinite damage. 

The impact of Accuracy is very hard to quantify, but it's things like this that make it hard to say "just get some ACC and stack damage", because what exactly is enough ACC? In a lot of fights, one extra miss can cause that enemy to survive one additional attack, which you then need to waste one full attack of 5 hits to kill off that enemy, or more if multiple dolls attack the same target. At the same time, there are enemies like Guards and Aegis that does not have any EVA. These enemies are relatively common, and you get no benefit from any additional ACC you have gained, which can be crippling if you sacrificed any damage for it.  

Exodia lineups are most susceptible to this, as their damage is focused on one strong attacker. Whenever a miss occurs, they are forced to waste a shot on the same target. The popular choices do have some way to counteract this, however. IWS tends to ignore the shields and snipe the backline, who tends to not have 5 links, giving her some leeway. Additionally, she comes with 79 base ACC with +50% from M950A. G11 attacks 3 times when her skill is active, reducing the effect of each bad roll, and often allowing her to kill enemies despite having multiple misses due to the number of hits. Additionally, she can be buffed by SAA and/or K5, giving her 40% to 90% ACC on her lower 44 base ACC.

Some additional very specific situations where ACC can screw you over. 

• An enemy with 2 dummies and 100 hp each can survive an attack from 5 dummies with 80 damage if 2 of the 5 attacks missed.
• An enemy with 5 dummies and 100 hp each can survive 2 attacks from 5 dummies with 80 damage if 1 of the 10 attacks missed. This value is true for any damage value between 50 and 99. 
• An enemy with 5 dummies and 100 hp each can survive 3 attacks from 5 dummies with 80 damage if 2 of the 10 attacks missed.

3. Criticals

Similar to Accuracy, having a hit not critical can cause you to waste extra attacls killing off a dummy you could have killed (if you have critted that hit). This damage variance is also why 100% crit rate can be very strong. If you have a 100% crit rate, you have one less factor that can interfere with calculations/estimations, allowing you to minmax things more. 

You can still get screwed over by misses, though, but this can be less of an issue if the enemy has less than 5 dummies, as if you can one-shot an enemy dummy, you can afford 1 or 2 misses on enemies with 4 or 3 dummies. 

4. Multiple Grenades

The largest issue of multiple grenades is not actually link protection, but in a case where you have multiple weak grenades that could not completely kill of enemies, some of the grenades will likely be affected by link protection in some form (in addition to dealing less damage from enemies having fewer dummies). This is most evident with FAL. 

Some grenade salvos can still clear enemies, however, since an enemy with only one 50 hp dummy can still die to a 80 damage grenade. 

5. Multi-hit units

G11 deals 15 hits per attack instead of 5 hits that do 3x damage. This means that critical variance, missing and link protection, in general, affects her less. This goes for every unit that deals multiple hits, including ST-AR 15 MOD3, which is another small reason why the MOD is so impactful despite the secondary hit dealing very little damage. (There are many other reasons as well, but this is a small part of it.)

Multi-hit attacks do have the issue of being affected by armor multiple times, though, so that's the trade-off. 

6. Golyats (Goliaths/Black or Red Beans)

They ignore Link Protection. They don't ignore heavy damage protection, but that's why they often come in multiples. Some other attacks that are made to instantly kill you also ignore Link Protection.

Sources#

CN: https://bbs.nga.cn/read.php?tid=15377235&rand=296 

KR: https://gall.dcinside.com/mgallery/board/view/?id=micateam&no=594130