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FGO Mechanics: Instant Death

by Firq • Published on 19 August 2023

While writing this, Requiem and I faced a bit of a challenge concerning death rate calculations. Case in point is the passive “Item Construction” and its interaction with Instant Kill, as we could not reach a final verdict if it affects Instant Kill Hit rate or not. In case of this article, I will assume it doesn’t interact with the hitrate, but if you have proof that this is different, I will gladly incorporate this in the article.


Instant Kill & Instant Death: One of the most rejected systems to exist in FGO. Most players know of it, but discard it because of its unreliability and uselessness against stronger enemies. In this article, I want to dive a bit into the workings of Instant Kill and help you understand how you can, in specific scenarios, use it to your advantage.

There are a multitude of servants that have access to instant-kill, but I will only highlight a few here (You can view the full list on Gamepress)

But since Instant Kill is based on probability, most players are relucatant to use it in their farming compositions. This thems from the different death rates enemies have:

This list here is just for rarities. However, there are a lot more factors to consider, as some enemies have higher death rate, some lower. Be sure to check each case individually, as rates may vary.

Also, servant enemies usually have a death rate of 0.1%, sometimes a bit more like 0.3% or 0.4%. So going for Instant Kill on servants will, in the majority of cases, not work.

Calculating Instant Death Rate

The formular for getting the probability of an enemy dying to Instant Kill is as follows:

death = hitRate * deathRate * (1 + instantDeathRateUp - instantDeathRateDown - instantDeathResistUp + instantDeathResistDown)

The parameters here are the following:


The main reason this came up was because of a farming comp used in Hunting Quest XI - Day 5 - Pride+. The node is structured into a 2 - 1 - 1 Layout, meaning using a dual-DPS setup would be the way to go.

Looking at the stats for the first wave, it made sense to use Nitocris: Both Ghouls have a 100% Death Rate according to Atlas Academy.

I went with using Nitocris, since she has a 100% NP charge and a skill that increases her Instant Death rate by 100%. Not needing any additional charge meant that no other buffs or AOE charges needed to be used on turn 1.

Her kit brings the following stats:

Actual calculation

When using the formular from above, we have the following values

hitRate: 50%
deathRate: 100%
instantDeathRateUp: 100%
instantDeathRateDown: 0%
instantDeathResistUp: 0%
instantDeathResistDown: 0%

This means we can fill in the formular like this

death = 0.5 * 1 * (1 + 1 - 0 - 0 + 0)

We now break everything down step by step

death = 0.5 * (1 + 1)
      = 0.5 * 2
      = 1
      = 100%

So her death succeeds 100% of the time on these ghouls, which makes her perfect to use in this scenario.

For other skill levels, this looks like this (Her S1 scales from 50% to 100%)

 Skill Level |  1  |   2   |  3  |   4   |  5  |   6   |  7  |   8   |  9  |  10  
 Death %     | 75% | 77.5% | 80% | 82.5% | 85% | 87.5% | 90% | 92.5% | 95% | 100% 

In the end, this resulted in the following comp that worked like a charm.


This small article should have given you an insight into using Instant Death as an advantage in the future. But remember: Stacking Gacha in a Gacha game can backfire.

That’s all for now, thanks for reading ~ Firq