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How does spell disruption work?

Ok so I see that an alteration spell is being cast, I want to disrupt that spell via damage (melee, range, energy or arcane damage), I hit, sometimes the spell is disrupted and sometimes the spell caster carries on and casts anyway.

I am genuinely curious to know:

- What is the chance to disrupt a casting via damage?
- Does the level of the caster make a difference?
- Does the damage type make a difference? I rarely ever see poison failing to disrupt a spell, is this because it often acts so many times per round or does it actually have a higher chance to disrupt?
- Does the caster type (cleric, druid, sorcerer or mage) make a difference?
- Does what they cast from (scroll, innate, arcane/divine spell-book) make a difference? I recently read an @semiticgod post about the acid kensai saying scrolls are harder to disrupt (which prompted this topic) if so, what is the % difference in chance to disrupt.

I used to believe, way back, that clerics were harder to disrupt than mages and often used other means to avoid their spells than damage disrupting, whereas mages I would happily disrupt via damage providing I had gotten past whatever protection was needed to do so. Recently however (since EE) I seem to disrupt clerics just fine. Was this belief mistaken all along or did EE change anything in that regard?

I know some casters have undisruptable spells, generally I am not talking about these, although it would be useful to know who they are. Mulahey, I believe is one.

TLDR: What are the mechanics behind the chance to disrupt a spell via melee, range, energy or arcane damage?

Thanks in advance!



  • semiticgodsemiticgod Member Posts: 14,506
    In my experience, any form of damage, even if the caster is immune to it, will disrupt a player character's spell, unless it came from a scroll, in which there was no chance of disruption. The amount of damage was not relevant. An enemy spell, however, could be difficult or impossible to stop depending on its script; there are functions that guarantee successful spellcasting despite damage or even 100% spell failure.

    In vanilla, ToBex could determine disruption via a formula, but EE I've heard has no such mechanism. In my experience in EE, I have found poison only occasionally disrupts enemy spells, but it depends on the script rather than chance: if an enemy got hit once during the casting of a spell but did not get disrupted, it could also get hit several other times without getting disrupted.

    I don't know how the ToBex formula worked. I'll tag @Demivrgvs in case he knows.

  • GandaGanda Member Posts: 35
    Interesting, so the times I have hit enemies and not disrupted their spells would all be because that particular enemy and spells script has immunity to disruption. Otherwise it should disrupt 100% of the time on hit?

  • GandaGanda Member Posts: 35
    As a normal player in game, I would have no real way of knowing if a spell was being cast from a scroll or has a script that makes it immune, other than meta game knowledge, I presume.

  • Lord_TansheronLord_Tansheron Member Posts: 4,198
    What I find most interesting is that sometimes I can disrupt the very same spell and sometimes I just can't. There's some fights where I reload a lot, and face the same sequence of enemy spellcasting at roughly the same time - and sometimes my damage will interrupt it, while other times the same damage on the same character casting the same spell at the same time will not do it.

    Could be my mods, though. Not sure if SCS does anything like give extra interrupt resistance, or choose randomly whether a spell is cast from scroll/script. It's not a very common occurrence, but it does happen.

  • DemivrgvsDemivrgvs Member Posts: 315
    edited January 2016
    @semiticgod summons Demi and Demi answers. ;)

    ToBEx Concentration check works like this: if (1D20 + luck) > (spell level + damage taken) then you can still cast the spell.

    No idea why EE left so many cool ToBEx options out. :( Anyway, without ToBEx concentration simply does not exist - any dmg taken disrupts spellcasting - unless (as you pointed out) AI is scripted with "reallyforcespell" which makes the spell impossible to disrupt.

    @Lord_Tansheron I think SCS seldomly use scrolls and even wands (both not interruptable). I'm not 100% sure on this though because I stopped playing ages ago and I barely have the time to mod.

  • GoturalGotural Member Posts: 1,229
    I'm going to add to this discussion that Clerics are harder than Mages to disrupt.

    I have no proof but is is a strong feeling I got from all these years playing Baldur's Gate, even in my most recent run, my Blackguard could ignore spellcasting interruption about 1/4 of the times.

  • GandaGanda Member Posts: 35
    @Demivrgvs So in ToBEx the higher the spell level and the more damage taken, the less likely it would be to save a concentration check. I agree this so should have been in EE!

    @Tresset That sounds complex! As you pointed out, so odd it would appear to be a bug if correct.

    @Lord_Tansheron That is pretty much how I felt, like sometimes the same spells were disrupted and at other times not. But I must admit to not having done any kind of systematic and thorough testing.

    I just did a small test using my own multiplayer party and as @semiticgod said, I got disrupted 100% of the time (20 out of 20) while hitting my own party casters (a cleric and a mage) with my own party members.

    Have not tested on enemy casters yet at all though.

  • GandaGanda Member Posts: 35
    Gotural said:

    I'm going to add to this discussion that Clerics are harder than Mages to disrupt...

    This is exactly how I felt, especially back before EE. Since EE though I have got the feeling or impression that Clerics seem to get disrupted via damage far more easily.
    I know Clerics will have better AC, but in the past I could swear to seeing them hit many times and not having their spells disrupted.

    I can't think of many sure fire times enemies have been uninterruptable, I know Mulahey as an example is, or at least his first spell is. How about the Amazon's after the Naskel mines, I'm pretty certain I have seen them being hit for damage but continuing their spell casting.

  • MusignyMusigny Member Posts: 1,018
    If you want to experiment, you need to know how the spell casting is scripted. As already mentionned in this thread, there are script actions which will force the spellcasting anyway.

  • GandaGanda Member Posts: 35
    Musigny said:

    If you want to experiment, you need to know how the spell casting is scripted. As already mentionned in this thread, there are script actions which will force the spellcasting anyway.

    Experimenting for me is unfortunately limited to in game only (no editor) as I play on android. My knowledge of how a game engine works and stuff behind the scenes is pretty terrible too. Hence the initial question I guess, hoping others with better computer magik than me could confirm or deny.

    I'll be in game experimenting though ;)

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  • GoturalGotural Member Posts: 1,229
    @subtledoctor The chance is definitely not 100%, I had my own character avoid spell disruption many times, especially my Blackguard in ToB when he was casting divine spells.

  • MusignyMusigny Member Posts: 1,018
    @subtledoctor's example tends to collapse his own theory as the mad cleric west of Beregost uses a generic script with 4 interruptible spells.
    0 or 100% might be the real intent but it seems the engine reacts differently. Btw the log tells you if there is a spellcasting failure, not the graphical animations.

  • KaigenKaigen Member Posts: 1,567
    That said, I have had spellcasters get interrupted by getting hit by an effect whose damage they were 100+% resistant to, so I think there's some weight to the theory that interruption is linked to something other than the damage itself.

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  • GoturalGotural Member Posts: 1,229
    I agree than when you don't get disrupted, there is no damage animation, only the blood effect.

    What I can say for sure when I don't get interrupted is that:

    -I start to cast
    -the casting animation is going on
    -I take some damage
    -the damage appears in the combat log (I think this is important, I'm sure I suffer some damage during the casting)
    -I don't get the damage animation, only the small blood one
    -my cast continues

  • MusignyMusigny Member Posts: 1,018
    A screenshot with no ambiguity, taken while play-testing Tactics - The Yuan-Ti mage casts chaos with a simple Spell() action via a custom script:


  • GoturalGotural Member Posts: 1,229
    Thank you for this screenshot @Musigny !

    I had a few screenshots of my Blackguard in ToB to prove that but I deleted everything after my last report on the no-reload thread sadly.

  • jesterdesujesterdesu Member Posts: 373
    Bassilus is an example of somebody who will sometimes be interrupted and sometimes not, when casting the same spells. I've seen it multiple times whilst he's been affected by poison. I've interrupted as much as all and as few as none of his spells whilst keeping him constantly poisoned and witnessing him taking damage during each cast (bgee no mods).

    I don't believe that all are either 100% or 0% chance.

  • [Deleted User][Deleted User] Posts: 0
    edited February 2016
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  • GoturalGotural Member Posts: 1,229
    I was so happy when I read that :smiley:

  • MusignyMusigny Member Posts: 1,018
    Gotural said:

    I was so happy when I read that :smiley:

    I am a bit less enthusiastic for two reasons:
    - Spellcasters, mages in particular, are already the most difficult foes. reciprocally your own spellcasters are often the most powerful members of the team. I wouldn't like to see this game turning into a list of mage battles.
    - Introducing concentration checks should not hide the current phenomenon. I don't call it "issue" or "problem" as this is still subject to interpretation. However something has to be assessed and fixed before trying to introduce something new.

    I hope that
    a) they are going to make it optional and
    b) a log entry will clearly indicate the concentration check result.

  • BongrizBongriz Member Posts: 6

    Well, word just came down that the SoD patches will give us the option for concentration checks to avoid disruption. So however it works now, soon we'll be able to make it work according to an actual *known* formula! (And the formula is such that the chance for disruption is related to the amount of damage taken... so massive wallops with Crom Faeyr will work better than little nips from a dagger or poison or insects.)


    I’m very curious as to how spell interruptions worked previously and how they work now, both in theory and practise. I’ve included a link below to a thread discussing the topic, but I don’t entirely understood the interpretation. As far as I’ve been able to piece together from reading these fora, spell interruptions worked like this previously:

    *Any lvl spell would always fail if the caster was hit, regardless of the lvl and class of the caster and regardless of the amount of damage being dealt. The exceptions to this were spells cast from items or force-scripted spells.

    This previous implementation made for very frequent interruptions, even dealing 0 damage. Use of poison or insect swarm was very effective due to the many hits per round.

    As far as I can understand, spell interruption has been implemented like this now:

    *When a caster is hit while casting a spell, there is a chance that the spell will be interrupted. The likelihood of interruption increases with the lvl of the spell being cast and with the amount of damage being dealt. Presumably, spells cast from items and force-scripted spellsstill cannot be interrupted.

    This new implementation reduces the frequentcy of interruptions, especialy concerning low-but-frequent damage-dealing tactics, such as poison or insect swarm. According to the thread I’ve linked to, interruptions are almost impossible now, even when exorbitant amounts of damage are being dealt.

    Can anyone provide some further insight to this?

    Quoting from this thread:

    Spellcasting Failure (16669)
    The way that spellcasters fail after taking damage has
    been externalized to CONCENTR.2da. By default, any
    damage a spellcaster takes will cause them to fail their
    0 Any damage
    1 (1d20 + luck) vs. (spell level + damage taken)
    2 (1d20 + Concentration ) vs. (15 + spell level)
    Note from the Developers: This is inspired by a feature
    from ToBEx. Be aware that Baldur's Gate games have
    no Concentration skill; using that option will use a basic
    1d20+luck formula for the caster's check.

    The file has this by default:
    2DA V1.0

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  • ThacoBellThacoBell Member Posts: 11,901
    @subtledoctor "
    The smaller change cane with v2.5.17: before, casters were interrupted when hit, even if the hit did zero damage. (Think, caster with 100% fire resistance being hit by a Fireball.) This was wrong and dumb. "

    Not necessarily. They only need to flinch to interrupt casting. I could walk up and blow in a casters face and hurt them at all. But if they flinch, its a perfectly valid interrupt.

  • semiticgodsemiticgod Member Posts: 14,506
    Even then it wasn't consistent. Taking zero damage from a Fireball because of Protection from Fire cost you a spell; taking zero damage from an arrow because of Stoneskin cost you nothing.

  • Abi_DalzimAbi_Dalzim Member Posts: 1,410
    Well, there's a distinction between "X is immune to my damage" and not registering any damage. So Protection From Fire won't prevent spell disruption from a Fireball, but Globe of Invulnerability will. Insofar as the interruption is determined by the animation of taking damage, at least that's internally consistent.

    My problem is that even when targets take damage, there's still way too much inconsistency regarding whether they'll be disrupted. I've died to Bassilus so many times because he was able to cast Hold Person through my damage, only to reload and succeed in disrupting him the second time around. And you'll occasionally see that with other characters as well, or even your own player characters, who can sometimes get lucky on that and cast through damage.

    And really, I consider this to be the single biggest technical problem with the games right now. Casters are supposed to be limited by the danger of having their spells disrupted by damage. That's part of the intended game balance, so when it doesn't work, it makes enemy casters more threatening than they're supposed to be. I would really, really like this to get fixed at some point, because I honestly think it would transform how the game works on a fundamental level, given how widespread this problem is.

  • semiticgodsemiticgod Member Posts: 14,506
    @subtledoctor: Wasn't there something about clerics and druids not being affected by spell disruption? I've focused do much on the disruption of mage spells that I don't actually know if there's any truth to that.

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