2d6 Vancian Variant

That 2d6 fantasy game began as a variant spell casting system for plain old D&D. As much as I like that complete system, I still think a 2d6 variant for the standard magic-user would be useful. Jeff has already done the heavy lifting, but here is some further discussion and systematization.

The traditional game differentiates between magic-user class level and spell level (to the consternation of many a beginning player). For example, magic-users can’t cast second level spells until they are third level. The highest level spell is almost generalizable to magic-user class level divided by two and rounded up (but not quite, because sixth level spells can’t be prepared until twelfth level). For the purposes of this post though, we can rationalize this to make up a new stat “magic bonus” which is magic-user class level / 2, rounded up. Call it M.

The rules:

  • Magic-users can prepare up to M spells (doesn’t matter the spell level)
  • Casting a spell of level L in armor A: 2d6 +M -L -A
  • Spell is lost (must be re-prepared in controlled circumstances) on 5-
  • Spell is retained after being cast on 6+

For adjudicating the various levels of success, consider the following guidelines. For catastrophe (2 or less), some effect should occur that is approximately as negative to the caster (or positive to the caster’s enemies) as would have occurred had the spell gone off as expected. A backfire (doing full damage to the caster) or the summoning of a hostile creature rather than an ally are classic examples. Miscasts (3-5) should lead to some minor inconvenience that is thematically consistent while achieving none of the intended goal. Delayed success (6-8) may also be interpreted as immediate but reduced. Immediate success (9-11) is casting as normal, with no adjustments. And finally, puissant success (12 or higher) could have extra duration or maximum damage. I don’t think tables of exact results are needed for impartiality; a player should know the level of danger by inverting the potential benefit.

The following is a table showing the chance of 6+ (delayed success or higher), by magic bonus (which is a proxy for class level) and spell level (which is a proxy for magic difficulty). The first column (with the plusses) is the bonus, the first row (with the minuses) is attempted spell level. Thus, for example, a character with a +4 magic bonus (magic-users of level 7 or higher), has a 58% chance (6+ on 2d6, +4 from the magic bonus and -5 from the spell level) to be able to cast a fifth level spell with partial success (full success, consulting the magic table above, requires a 9+). All percentages are rounded, and taken from anydice.com (click on the “at least” button).

Chance of 6+ (required for partial success)
Magic Bonus -1 -2 -3 -4 -5 -6
+1
72
58
42
28
17
8
+2
83
72
58
42
28
17
+3
92
83
72
58
42
28
+4
97
92
83
72
58
42
+5
100
97
92
83
72
58
+6
100
100
97
92
83
72


This system has the following benefits, in my opinion. No stupidly large number of spell slots to fill for higher level magic-users. Vance’s spell casters were not able to cram more than a few spells into their consciousnesses. Also, it allows lower level magic-users to cast higher level spells with a decreased chance of success even more elegantly than some previous Vancian variants I’ve experimented with. The magic bonus M along with the fivefold casting result chart replaces the original spell slot chart. The armor penalty to casting obviates the need for armor restriction in a finer grained way that other “arcane failure” systems I have seen (light armor makes a character function as if she were 2 levels lower, medium armor 4 levels lower, and heavy armor 6 levels lower).

Those who have been paying attention may notice some similarities with the DCC RPG wizard system. That also uses a relatively smaller number of spells, though more than I have here (up to 16 at level 10). It uses a d20 roll to cast, with caster level as bonus, and a difficulty class of 10 + (2 * spell level). This is nice, but I prefer 2d6 because it makes (for example) the difference in difficulty between a second and third level spell greater than the difference between a first and second level spell. Also, the crit and fumble chances with 2d6 are 1 in 36 (about 3%, assuming balanced modifiers), and they scale up nonlinearly with difficulty.

A minor point: that multiplier of 2 in the casting difficulty class formula for DCC RPG is an indicator of a system kluge. The two parts of the system (class level and spell level) don’t really fit together. The same thing is true of my 2d6 formulation as well, but at least you only see it once per level up (when you potentially recalculate the magic bonus), rather than on every casting check. Further, as casting spells is really all the magic-user gets better at, there’s no real reason not to just change the experience progression so that level 6 is equivalent to the old level 11 or 12. Thus, one might have an experience progression of 0, 5k, 20k, 50k, 100k, 300k. Then magic bonus, class level, and spell level are all on the same scale.

If you’re playing B/X (or a system with comparable intelligence modifiers) feel free to add the intelligence bonus to the magic bonus for purposes of the number of spells that can be prepared (but probably not to the actual casting check, as that would be very powerful). If you want magic to be a bit harder, have the magic bonus increase in steps of 3 levels rather than 2 (that is, level / 3 round up). For extra fortifying play, consider letting starting magic users randomly determine the level of starting spells in addition to the spells themselves (probably good to let them start with at least a few first level spells though). Or might I suggest a grimoire system?

Here are a few more charts of probabilities, to illustrate the dynamics of the system.

Chance of 9+ (required for standard success)
Magic Bonus -1 -2 -3 -4 -5 -6
+1
28
17
8
3
0
0
+2
42
28
17
8
3
0
+3
58
42
28
17
8
3
+4
72
58
42
28
17
8
+5
83
72
58
42
28
17
+6
92
83
72
58
42
28


Chance of 2- (catastrophe)
Magic Bonus -1 -2 -3 -4 -5 -6
+1
3
8
17
28
42
58
+2
0
3
8
17
28
42
+3
0
0
3
8
17
28
+4
0
0
0
3
8
17
+5
0
0
0
0
3
8
+6
0
0
0
0
0
3

8 thoughts on “2d6 Vancian Variant

  1. Random Wizard

    The 2d6 system got me to thinking about what I don’t like about d20. And what I liked about the older ability score checks.
    I like systems where the success chances are displayed up front (like the 2d6 system). And then you modify the success by modifiers (usually small ones +1, +2) on the fly, as the GM accesses the situation.
    In the d20 system, you don’t have the chance of success displayed on the character sheet (or just know it) up front. The DM has to make up a target number.

    Reply
    1. Brendan

      @Random Wizard

      Agree. Also, I think that difficulty class systems often lead to “arms race” escalating dynamics between character bonuses and difficulty classes, unless that is very consciously controlled.

      Reply
    1. Brendan

      @Eric

      For bookkeeping simplicity, I was assuming that the magic bonus stays the same. Having one less casting option (in addition to the miscast or fumble result) seems like enough of a penalty. However, it would be easy enough to decrease the magic bonus too, if you want to reflect fatigue or something like that and don’t mind the bookkeeping. In fact, I have something similar to that outlined here:

      http://untimately.blogspot.com/2012/09/arcane-stress.html

      Reply
  2. -C

    Right. Excellent article.

    First, I am certain that this is the appropriate 2D6 distribution.

    In my last/current tabletop game (not Numenhalla) players used the vancian memory cell system from gorgonmilk. One side effect of this system (or the way I ran it at least) is that a spellcaster can cast any spell that is equal to his level or lower. Granted, they are limited in ‘brain space’ and sixth level spells take up huge amounts of space, leaving them with little room for anything else. It was not particularly disruptive to play.

    It bypasses the adherence to the old tables and is a truly separate new casting system. My questions are as follows. There doesn’t appear to be any resistance to casting – that is, the first cast is the same as the 10th. It is elegant and saves the recalculating. My question is, aren’t spells more powerful than swords? I’m not certain that I want casters casting the frequently. The issue of course comes in with the 5th level caster casting the 1st level spell. This makes the minimum result 6. This means 3d4+4 damage, automatically hitting in combat every round (average 11 points of damage at range). Isn’t the extra upkeep of the ‘resistance’ to casting multiple times worth it?

    Reply
    1. Brendan

      -C wrote: Isn’t the extra upkeep of the ‘resistance’ to casting multiple times worth it?

      It may well be. It’s hard to compare the two cases directly, as only being able to prepare M different spells limits the flexibility of the caster also. (Remember, M = level / 2 round up.) One minor modification which might address your concern would be to make snake eyes a fumble no matter what M is, leaving a slightly greater amount of inherent risk.

      Individual spells could also be tweaked as desired (ranged touch attack with bonus +M for magic missiles perhaps?).

      Reply
    2. Brendan

      A few more thoughts. Any modification to the spell casting system is likely to have some unintended consequences, as the rules for spells are the rules for bending reality. For example, the most important aspect of the original spell casting system is how it changes resource management and capabilities as level progresses. Come fifth class level, for example, fly is available (assuming you don’t excise it from the game), which totally changes the nature of challenges. See here for a more thorough treatment of this idea:

      http://1d30.wordpress.com/2011/11/22/magic-changes-resource-management-1e-add/

      The memory cell system that you describe results in a qualitative change in game play by allowing magic-users access to preparation of powerful spells pseudo-exponentially more quickly (because of how the experience progression works). In other words, 5000 XP is required to be able to cast fly rather than 20000 XP.

      That said, perhaps magic missile becoming at-will around 6th level is actually a feature rather than a bug, as it highlights the fact that the nature of the game changes at that level.

      Reply
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