From FFXI Wiki

Resists lower magic damage and/or duration of offensive magical spells, abilities, and weapon skills, and occur more frequently the lower the caster's Magic Hit Rate is. Any spell that does damage can be resisted in these increments:

Resist Level 0: 1/1 (No resist)
Resist Level 1: 1/2
Resist Level 2: 1/4
Resist Level 3: 1/8 (Full resist)

Additionally and unrelatedly, Magic Damage can be reduced by other factors, like target-specific magic damage reduction, Magic Defense Bonus, and target-specific elemental resistances.

Current Theory

Magical effects have a certain number of "Resist" states (as shown above for damaging magic). For some spells (like Sleep) a resist will affect duration. For others (like Elemental Magic) it affects damage.

Magical effects do not always have a full range of resist states. Some (again, like Sleep) only have Resist Level 0 (60 second duration) and Resist Level 1 (30 second duration).
Thus, the odds that you will successfully land Sleep on a monster follows the Two-State relationship on the left below. This means that you have a 99.75% chance of initially landing Sleep on a monster with capped Magic Hit Rate, but still only a 95% chance of landing it for the full duration, as shown on the graph to the right.
All Enfeebling effects with fixed duration follow this Two-State relationship. Other magical effects such as enfeebling effects without set duration (like Paralyze) or spells that have neither damage nor enfeeble effect (like Dispel).
There is insufficient testing/information to prove if there are multiple resist states or the exact determination of durations. Spells with a damage and enfeeble component calculate resistance and states independently for damage and enfeeble duration.

M resists States.jpeg
Resist state distribution.JPG
Relationship between Magic Hit Rate (X)
and Effect Land Rate (Y)
Relationship between Magic Hit Rate (X)
and Resist State Probability (Y)

These relationships were discovered through testing, which indicated that Magical Resist state is determined by an iterative process. So when you cast a spell, you have a certain Magic Hit Rate against the monster. The game generates a random number between 0 and 100% and compares it to your Magic Hit Rate. If the game's random number is higher than your Magic Hit Rate, you move up one Resist State and the game generates another random number to compare. So if it is higher than you once, you gets a 1/2 resist. If it gets higher than you twice, you get a 1/4 resist. If it gets higher than you three times, you get a 1/8 resist. If the spell you cast only has two resist states and the game beats your magic accuracy twice, then you just get a "___ resists the effects of ____."

This results in the following distribution of Resist states for magical damage:

This results in the following distribution of Resist states for 2 state enfeebles:

Roll Analogy: It's somewhat classic in FFXI probability to liken everything to a /random battle, so here goes!
Imagine that every time you cast a spell you're having a /random battle with the monster. Your "/random" is always equal to your magic hit rate × 1000, so a 95% magic hit rate would be a 950 roll. If the monster loses his first roll, your spell lands unresisted. If he wins his first roll, he gets to roll again. The number of times he wins determines the Resist Level as listed above. So two wins would be Resist Level 2, a 1/4 resist. Two wins against Sleep or Sleep II would be a full effect resist, because those spells only have a Resist Level 0 and 1.

Elemental resistance

Elemental SDT

Specific Damage Taken, formerly understood as "Species" Damage Taken, (now called SDT due to a gaffe on the BG forums) is a reduction or bonus in damage to an element (including breath and magical) or weapon damage type; as well as a resistance to enfeebling effects of that element based on the foe's specific SDT resistances.

  • Every monster in the game has values for physical and magical damage in tiers; see these tiers below.

Note: "Specific" Damage Taken was actually a spelling autocorrect error from the previous understanding of "Species", but we are running with it as it makes sense. NMs of the same species commonly have different damage resistances and vulnerabilities.

Aside from damage, SDT values also impact magic accuracy.

  • Anything above 50% will add a 1/2 resist after the fact to enfeebling magic or additional effects of the corresponding element.
  • No resist will become 1/2, with the other levels now becoming 1/4, 1/8, and 1/16.
  • For example, Ghosts and Skeletons are at the 50% tier and will take a 50% reduction from Element: Dark dark elemental damage.
  • Furthermore, they will be guaranteed to resist Sleep for example outside of a magic bursted Compression skillchain or Rayke with at least one Tenebrae rune as that will take the tier below 50%;
  • As previously mentioned, spells like Sleeps and Absorbs either land fully, have a half resist, or are completely resisted. Since Sleep may not fully land against these Ghosts or Skeletons, there is now only a single state to the spell see the roll analogy and chart above again.

SDT is separate from ordinary resists, and resist distributions (1/4, 1/2, or 1/8) do not change regardless of magic accuracy or the level of the foe; more on this below.

  • Immunobreaks are also separate and allow players to bypass these resistances as well as monster specific resistances for enfeebles outside of monsters SDT values.
  • Once again returning to Ghosts and Skeletons. There is more to resistance to enfeebles than SDT. Despite both sharing a 50% Element: Dark dark tier; skeletons are typically much harder to sleep than ghosts.
  • Furthermore, a monster like Maju has a significant resistance to Blind, but Frazzle will land without trouble by comparison. This ends up tying into the Immunobreak update, it seems like the system was just slapped over what existed as a fix.

  • Skillchain damage is reduced in accordance to an enemies SDT tier. This makes determining the exact tier of resistance possible.
  • While it is easy to determine the tier of SDT through skillchains, the conversion of this to the increase of resistance in landing spells is not the same as the tier value. Thus resistance values are currently unknown outside of certain tiers such as 5% immunity or 50% or lower guaranteeing resists.

What is it/what does it do?

  • It's been long known that monsters have varying resistances to different elements but due to the nature of magic hit rate testing not much headway has been made in trying to nail them down.

After the Jun 17th 2014 version update, resists on skillchain damage were removed and a damage bonus/reduction was added to skillchain damage based upon the target's elemental resistances (SDT). Because of this we are able to easily define elemental resistances of mobs in 15 specific tiers (exact quantitative values in terms of macc/meva have yet to be determined). And allowed us to discover what effects said resistances have.

SDT Tiers

  • Resistances are a multiplier to skillchain damage and are what this testing is based off of. The tiers for skillchain damage are:
Specific Damage Taken (SDT) Resistance Tiers
(High resistance) 5% 10% 15% 20% 25% 30% 40% 50% 60% 70% 85% 100% 115% 130% 150% (Low resistance)
  • These percentages are multiplied to skillchain damage.
  • For example performing Liquefaction on a fire elemental which has 5% resistance tier to fire will result in a skillchain damage that would be reduced to 5% of what it would otherwise do without this multiplier.
  • With skillchains with multiple elements tiers the elemental with the lowest resistance will be the element of which damage was taken.
  • In the case of a tie the following order decides: Element: FireElement: IceElement: WindElement: EarthElement: ThunderElement: WaterElement: LightElement: Dark
  • For instance, on an enemy with equal resistance tiers for all elements; Light SC Icon.png Light skillchains will be treated as Element: Fire fire and Dark SC Icon.png Dark skillchains will be treated as Element: Ice ice.
  • While a skillchain may only deal one type of damage, all corresponding elements of a skillchain have their SDT tier boosted by 1 during the 10 second Magic Burst window.
  • Skillchain tier bonuses do not stack and reset after each skillchain, but are counted before the next skillchain in a multi-step.
  • In other words Distortion SC Icon.png Distortion grants a tier bonus to water and ice. If you created Fusion SC Icon.png Fusion off of it then the bonus is now gone for water and ice and instead now applies to fire and light. Continuing into a Light SC Icon.png Light skillchain would consider the boost in tier from fire and light when deciding which damage to inflict and then apply a tier bonus to all elements associated with a Light SC Icon.png Light skillchain during the magic burst window.
  • For instance, your party is fighting a monster, lets call this monster Tanaka.
  • Tanaka has all 100% tiers as he is very baranced.
  • If a straight Light SC Icon.png Light skillchain is performed then the skillchain damage be fire. The same goes for performing a double light.
  • However, if a Fragmentation SC Icon.png Fragmentation skillchain is first performed followed by a Light SC Icon.png Light then wind has the higher tier over fire and comes before thunder. Therefore both skillchain damages would be wind.
  • If a double Light SC Icon.png Light skillchain is closed then the damage will once again become fire as all elements were of equal tiers after closing the previous Light SC Icon.png Light.

SDT and Magic Bursting

  • These ranks also effect Magic Burst damage. Percentages by rank are as follows:
Resistance Tier: 5% 10% 15% 20% 25% 30% 40% 50% 60% 70% 85% 100% 115% 130% 150%
Magic Burst Damage: +0% +0% +0% +0% +0% +0% +0% +5% +15% +40% +50% +60% +85% +115% +150%
  • These percentages are added into the damage bonus from number of steps then multiplied like normal.
  • For example normally a 2 step magic burst gives a 35% increase in damage. But on a monster with the lowest resistance to that element it would instead give a 185% increase in damage
    • Note, these bonuses do not apply to spells that normally wouldn't get a bonus from magic bursting (ie Breath Damage breath spells) and does not apply to Helix spells or Kaustra.
    • Note, due to the effects of the skillchain itself, the lowest tier isn't possible as the skillchain itself increases rank by 1.
  • For elements that are at 50% or lower the monster will have what has traditionally been call SDT (above) or specific damage taken to that element.
  • At 50% or less you are guaranteed a resist (1/8 → 1/16) independent of Magic Evasion or Magic Accuracy; even job abilities such as Elemental Seal.
    • Blackmage's Subtle Sorcery, while not reducing SDT works on a separate system; allowing full damage or effect spells against an enemy as low at the 20% tier.
      • However, this is not the case against lower tiers.
    • For elements that are at 10% the monster will have a high resist rate to that element. Magic hit rate appears to be set to 3-5%, even with Subtle Sorcery active. Distribution of resist states follows as normal otherwise.
    • For elements that are at 5% the monster will have a 100% full resist rate to that element independent of Magic accuracy or Magic evasion. Even Job abilities such as elemental seal or subtle sorcery will have no effect on this.

Affecting Values

The following will change the SDT tiers of a foe:

  • Rayke. For each rune expended will make the monster less resistant to that element by 1 rank.
  • Skillchains. During the magic burst window following a skillchain the monster will become less resistant to those elements by 1 rank.
    • This applies to all elemental damage including things that cannot magic burst such as elemental weaponskills, quick draw, or breath spells without Burst affinity.
    • For multiple step skillchains this resistance lowering will apply to the next skillchain but will not stack together. For example say you perform Liquefaction skillchain into Fusion skillchain. When determining which element to use for the Fusion skillchain and the damage multiplier for it the resist lowering effect on fire from the Liquefaction skillchain will be used. But during the Magic burst window after the Fusion skillchain it will only be using the resist lowering effect on fire and light from the Fusion skillchain. So at most skillchains can only make monsters less resistant to any one element by 1 rank each.
    • This stat is fundamentally different than the elemental resistance we see on the equipment screen. As such things like barspell, threnodies, or carols have no effect elemental resistance rank though they do effect the resistance to that element.

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