1. #1

    Players roll for Attack and Defense

    I was looking to try an old variant rule that lets the players roll for Defense when attacked by an NPC. Other systems use this method, and some of my players like how it keeps them more engaged when it isn't their turn. I'm having trouble figuring out how I could implement this with fantasy grounds. I want the PCs to actually roll the dice rather the be automated. Setting up something like a custom save (if that is even possible) wouldn't cut it as that would just be a convoluted (and automated) way to do what is already done with attack/ac. I am thinking it would be implemented like an opposed skill check, with the attacking NPC just having a fixed rather than random value. That could work, but is there a way to use the current AC (or current AC modifiers) as a modifier to a d20 roll? Ultimately, I would like to make a die roll that would be 1d20 + AC - 10 OR 1d20 + (AC Modifiers). Is there a way to point to AC in this way? Or is there a better way to implement this idea in general?

  2. #2
    Zacchaeus's Avatar
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    Hi Dradicus, welcome to FG.

    I'm sure you could do this if you created an extension but I wouldn't know how you would go about doing that.

    Without an extension you'd need to do it manually since there isn't a mechanism within FG to allow it. The players could add a modifier to the modifier box on the bottom left (being the AC-10 or AC Modifiers or whatever) and then roll a d20 to get a result. You would need then to compare that result with the attack roll (I assume - I'm not familiar with this defence roll idea).

    All this of course will throw out all of the basic mechanics of 5e and give extremely unpredictable results. (Again this assumes I am understanding what you are talking about).
    If there is something that you would like to see in Fantasy Grounds that isn't currently part of the software or if there is something you think would improve a ruleset then add your idea to the wish list http://fg2app.idea.informer.com/

  3. #3
    It works the same way as when an enemy spellcaster casts a spell with a DC (except not automated). Using the same bonuses as the regular Attack/AC operations, it just lets the player be the one involved with the roll.
    The odds can be kept the same as the regular interaction. Here is a quick post: https://rpg.stackexchange.com/questi...ls-for-defense

    The question I have is just that. How do you actually use AC as a modifier? I don't want the PC to have to type in their AC modifier in the modifier box every time they get attacked. I'd like to set up a .. power? custom dice? Something along this line that does the 1d20 + AC Modifiers roll, but I don't know how to directly reference the current AC value from the PCs character sheet.

  4. #4
    Trenloe's Avatar
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    Welcome to the forums Dradicus.

    Here's a thread where this has been discussed briefly before: https://www.fantasygrounds.com/forum...t-AC-extension
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  5. #5
    Zacchaeus's Avatar
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    So if a PC has a current AC of 16 (being 10 + Dex + Armour) you want to change that to 6? If so then an effect of AC: -10 would accomplish this. However I can't really think of any way to make the NPC roll a d10 rather than a d20 for the attack roll. You can obviously just roll dice into chat but that wouldn't register as an attack roll since it isn't being made from the attack string on the CT.

    I'm probably just not understanding what the point of this is to be honest; but I can't see a way to do this with any sort of automation. I think it would need to be an extension (and a fairly comprehensive and complex one at that) or you do all combat rolls manually as above.
    If there is something that you would like to see in Fantasy Grounds that isn't currently part of the software or if there is something you think would improve a ruleset then add your idea to the wish list http://fg2app.idea.informer.com/

  6. #6
    Thanks for the link, @Trenloe. I'm not sure if what it contains is very helpful to me though (nor in the followup discussion further linked in the Pathfinder ruleset). The big difference is I'm not trying to make that replacement for all situations. For PC vs NPC, PC vs PC, and NPC vs NPC, I want to be able to use the FG system normally. I'm only looking to have a PC roll for "defense" when specifically attacked by an NPC. I'm just looking for a way to reference the AC or modifiers directly from the PCs character sheet for use in a power or something similar
    Last edited by Dradicus; January 12th, 2020 at 12:59.

  7. #7
    Sorry, @Zacchaeus, but that is not my intention. I am specifically looking for it to not be automated. For a defense roll against an NPC attack, I want the player to use an ability/roll their dice in response to me declaring that attack. I may say something along the lines of, my orc is attacking with a 19, roll for defense. They would then roll their 1d20 + 6 (for the AC 16 example you gave). A 19 or higher would mean they successfully dodged the attack. I am aware that I could have the player type in a +6 in the modifer box to do this every time they need to make a roll, but I am looking for a way to build it into a power or something similar to reference their current AC to automate the modifer part of the roll (but not the action of them actually rolling the dice).

  8. #8
    Zacchaeus's Avatar
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    Ok, well there may be a couple of ways you could make such a roll. You could create a skill and just make the bonus the same as the AC bonus that the PC has (you'd need to amend that on level up/change of armour etc). Or maybe you could set up an action or weapon attack with just the AC modifier as the bonus. In either case the PC would be rolling a d20 and adding in the AC bonus.

    I can't think of any way to do it via effects (you can use AC: x in effects to alter the AC); since there isn't a concept of defence rolls built into the ruleset. As you mentioned in your first post the only such roll is a saving throw which I don't think could really work in this case.
    If there is something that you would like to see in Fantasy Grounds that isn't currently part of the software or if there is something you think would improve a ruleset then add your idea to the wish list http://fg2app.idea.informer.com/

  9. #9
    Assuming Im not misunderstanding/miscalculating something, you could also let them roll 1d20 for their defense roll (instead of an enemy attack roll).

    1. (automatically) x = 1d20-(21-AC)

    2. (manually) Hit if x <= Attack Bonus of Enemy (or Miss if x > Attack Bonus of Enemy)

    Explanation:

    Currently assuming PCs AC is 0 and the enemy attack bonus is 0 (will change).

    Assuming we still want a 20 to be good for the player, we need it to be bad for the enemy. We can achieve this inversion by simply calculating 21-1d20 a nat 20 from the player results in a nat 1 by the enemy (Why 21? A 20 would result in a range of 0-19, not 1-20.)

    As most FG mechanics assume a 1d20 + Fixed number, we unfortunately have to switch our formula around to 1d20-21, potentially resulting in a negative value.

    Factoring in AC:

    Now we just have to factor AC in, so in the regular system with an AC of 16, only rolls of 16-20 would hit in our inverse formula 1-5.

    We can do this by subtracting the AC from 21. In our example 21-16 is 5, so 1d20-5.

    5 should hit, 6 should not.
    1d20-(21-16)
    1d20-5
    a. 5-5=0 b. 6-5=1
    a. 0<=0 -> Hit b. 1>0 Miss

    Were currently still assuming the enemy attack bonus is 0, so any roll that results in a 0 or lower still hits. 5-5=0, 4-5=-1, , so that still holds true.

    Factoring in enemy attack bonus:

    This probably would have to been manually but you can just compare the result of the roll with the enemy attack bonus.

    Let us assume the enemy has an attack bonus of +5 (so 50 % hit chance against AC 16 as in the regular system, the attack hits on an 11-20).

    To test whether the formula holds up:

    AC 16, attack bonus of +5, in the regular system 10 should miss, 11 should hit, in our inverse system, a roll of a 10 (a) should hit, a roll of 11 (b) should miss.

    1d20-(21-AC)
    1d20-5
    a. 10-5=5 b. 11-5=6
    a. 5<=5 Hit b. 6>5 Miss

  10. #10
    @stephan_ Thanks for your input. This is precisely the sort of system that was being considered. It is a slightly different implementation that is mathematically equivalent, but I hadn't really thought of this approach. It may be easier to make a single calculation rather than two. What the variant used before was to add +11 to ATK and -10 to AC (which is the same as -21 to AC). The advantage of using -21 is you only have to make a single calculation. The advantage of the +11 and -10 would be that the numbers match the normal systems expectation, which I may still like better since the PCs are still using the regular system to attack the NPCs. This way it doesn't feel as much like two different systems. If you for instance roll a 19 for defense and are familiar with playing 5E, you have a good intuition of how good that is (since it correlates to the rest of the d20 rolls for skills/attack/dc/etc).

    It seems that from the replies that there isn't a way to directly access the current AC modifiers or total AC either one, so we'll just have to make an attack/power with a manually edited number that will just need to be updated if a condition affects their current AC (buffs/new piece of gear/magical item/level up/etc)

    Thank you all for your input and help.

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