Category Archives: Game Design

Spell Mishaps

It’s pretty well known that many of the conventions within D&D were directly inspired by works of fiction drawn from Gygax’s famous Appendix N.  Arcane spell-casting within D&D was very much influenced by people Like Jack Vance, L. Sprague de Camp and Fletcher Pratt.

In Vance’s Tales of The Dying Earth series wizards memorized their spells, and once cast, the memory of it was stripped from their mind.  As a wizard grew more powerful, he or she could memorize further and ever more complex spells.

In the works of de Camp and Pratt magic was precise and formulaic, a bit like alchemy except that instead of combining solutions it combined spell components in the form of various material, verbal, and somatic elements.

These of course have all become mainstays of spell-casting within D&D and many other fantasy RPGs. What was not included in D&D was the element of unpredictability in spell casting present in these original sources.  A faulty memory, a mispronounced word, a lacking material component, an imprecise motion were all things which could cause the spell to go awry in various ways leading to sometimes amusing sometimes calamitous effect.

This is something I’ve always felt was sorely lacking in D&D and other fantasy RPGs I played growing up, and it’s one of the things I’ve attempted to incorporate into my own homebrew RPG. Recently I stumbled upon a couple of other notable examples of spell mishap systems.  First I’ll discuss how spell mishaps work in my system, and then I’ll outline how they work in the two other systems I’ve recently discovered.

Spell Mishaps In Mythbinder:

In the system I’ve devised there are two conditions under which a spell might go awry. The first of these is whenever a caster’s attention might be compromised.  Casting while atop a galloping mount, or receiving damage while in the midst of enacting a spell are both prime candidates. However these aren’t the only things that might distract the caster. ongoing conditions such as fatigue, nausea and fear effects can each cause the caster to err in performing a spell.  To determine whether the spell is cast successfully the caster must make a Wisdom attribute check (1D20 + WIS modifier vs DC 15 + Spell Level).  If unsuccessful the spell is lost.  If unsuccessful by 5 or more the caster has to roll D100 percentile dice on the “Arcane Mishaps From Spell Failure” table (shown below).

The second way a spell can go wrong is if the caster is attempting to cast an unknown spell.   In Mythbinder a mage is not entirely restricted to their list of known spells.  They always have the option of trying to attempt to cast spells they don’t yet know.  These could be spells that they have seen others cast before, spells that they’ve merely heard of, or altogether novels spells which they discover.  Doing so, as you might imagine, caries a degree of risk, and there’s a lot of room for error.  When attempting to cast an unknown spell the caster must first make an Intelligence attribute check, the difficulty of which is determined by their prior acquaintance with the spell.  If the caster has witnessed the spell being cast at some point, then the difficulty class for the Intelligence check is 15 + Spell Level.  If they’ve merely heard of the spell before, the DC is 20 + Spell level.  If they are experimenting with an altogether new spell, the DC is 25 + spell level.  Failing this check means that the spell was unsuccessful, and all spell points needed to cast the spell (yup, I’m using a mana system) are spent.  Failure by five or more results in a spell mishap determined by the “Arcane Mishaps From Spell Failure”.

Arcane Mishaps From Spell Failure Table




The spell succeeds and the mage gains a permanent additional spell point.


Spell succeeds and is twice as powerful (double variable effects).


Spell succeeds but affects a random unintended target.


Spell fails but target is affected by a random spell of same level.


The spell succeeds but affects everyone within 25ft of the mage.


All of the mage’s spell points for the day are expended.


Mage is rendered unconscious for 1d4 hours.


 The mage is rendered comatose for 1d4 months.


The mage suffers from amnesia (a remove curse spell reverses this).


The mage suffers from madness (a remove curse spell reverses this).


The mage’s body is consumed in arcane fire (3d6 damage + scarring).


The spell succeeds but the mage permanently loses all spell points.


The spell fails and the mage permanently loses all spell points.


The spell succeeds but the mage dies.


The mage dies.


Dungeon Crawl Classics

I’m sure many reading this will already be familiar with the Dungeon Crawl Classics RPG, but I’ve just discovered that the RPG has a system of spell mishaps that is somewhat similar to my own.  According to the beta version (don’t yet own a copy of the final product) of this system, “Magic is unknown, dangerous, and inhuman.  Even the best wizards occasionally fail to properly harness a spell, with unpredictable results” (DCC RPG Beta Rules, p. 34).  Every time a wizard casts a spell, they have to make a spell check (1D20 + Level + Intelligence) vs the difficulty class of the spell (usually 10 + 2x the Level of spell).  Failure of this check means the spell is unsuccessful.  Critical success and failure rules apply to the roll.  A roll of a natural 20 is always a success and moreover results in a more powerful spell.  A critical fumble results in both a spell mishap (rolled on the Spell Fumble table), and a “corruption” of the wizard,  A spell fumble can be anything from transmuting an ally into an animal, to causing a rain of snails in the immediate vicinity.  A corruption is some bodily transformation of the wizard.  At its most benign this would consist merely in the wizard passing out for 1d6 hours.  At its worst this would take the form of a portion of the wizard’s soul being claimed by a demon lord, and all of the character’s abilities suffering a -2 penalty.

The Net Libram of Random Magical Effects

A guy by the name of Orrex has gone to a tremendous amount of trouble to assemble not one, but two volumes of random magical effects, each containing 10,000 entries! Many of these entries are rather creative and humorous.  Take for instance entry 0012 of volume 1, “”1D100 flies swarm from the caster’s mouth whenever he tells a lie.”  Or how about entry 3828, “pigeons react to the caster as if he were coated in bread crumbs.”  Others are more serious, such as entry 0002, “half of the caster’s body turns to sodium, the other half turns to ice.”  Orrex suggests a system for what’s causing these random magical effects having to do with unpredictable magical surges resulting from untutored attempts at magic (wild magic).  But these two 10,000 entry tables could also be used by themselves as say a supplement to the spell mishaps table that I created for Mythbinder, or the spell fumble/corruption tables that Dungeon Crawl Classics uses.

Magical Mishaps in the Notch System

The other day I suggested that the Notch system might offer an interesting alternative to Vancian and Mana magical systems.   Briefly, you determine when your caster is out of spells on this system by notches.  When a caster runs out of notches, they are out of spells for the day.  Notches in turn are determined by a roll of the dice.  Michael Kelley wanted to know if this system could be combined with a mishap system.  Of the two versions I suggested, one in which the die roll is made with different polyhedron dice keyed to the spell level, and the other made with a D20 with a DC that increased with spell level, I think the D20 Notch system is most easily adaptable to spell mishaps.  You could employ critical success and critical fail rules to the roll in the same sort of way that the DCC RPG does.  On a roll of a 1 you fumble and roll on the appropriate table.  On a roll of a 20 you gain an additional notch.

Well, that wraps up this post.  If anyone has any other suggestions about how to model a spell mishap system Id love to here them.