The Misadventures of Hareng Rouge

I am currently enjoying some tension with my Mutant Crawl Classics Judge about Natural 1s, Mutation Checks and Defects. We differ on the rules and whether the rules as interpreted by the Judge are fun. Needless to say, I am correct and in no way sulking about it.

The Rules as Written for mutation checks in Mutant Crawl Classics do not have a rule that Natural 1s result in an automatic defect

If you think they do, you have misread the rulebook.

I believe it is also Rules as Intended by the authors that there is no rule that Natural 1s result in a defect. Natural 1s on a mutation check in Mutant Crawl Classics do not result in a defect and should not result in a defect.

The Crawl Classics stable has codified Natural 1s and Natural 20s as a mechanical device in many but not all of the sub-systems. Explicitly in Combat, if you roll a Natural 20 you get a Critical Hit, with a nice table to roll on to see how you eviscerate your foe. If you roll a Natural 1 you get a Fumble, with a picturesque table to roll on to see you how badly you hurt your allies, or yourself. All good fun and games. There are other sub-systems were a Natural 1 or Natural 20 have mechanical effects. This appears to have created a folk ruling that Natural 1s in Crawl Classics game are always a Fumble in whatever sub-system you are rolling.

Sounds lethal, and it can be, but the Crawl Classics stables usually have some safeguards when you roll a Natural 1 that dampen the effect. That’s an important design feature to remember.

Mutation Checks and Defects

In Mutant Crawl Classics characters may have a mutation power that they to activate. They roll a d20 (usually), add some modifiers, look up the table for that mutation and apply the results of the roll. A result of 12+ gives you some beneficial results in a ladder of power and effect, a result of 2-11 gives you nothing, and a result – a result! – of 1 gives you a Defect. A Defect a mutation with an anti-mutation power or a mutation anti-power, a mutation sucking.

The Rules as Written

Rules as written; there’s obviously no obligation to play RAW.  I’m on record as stating that Mutant Crawl Classics isn’t well edited and is probably under play tested. As I read the rules, Mutant Crawl Classics does not include a general mutation defect fumble rule.  There is an equivalent in Dungeon Crawl Classics but not in Mutant Crawl Classics. I think the omission is probably intentional, particularly because Dungeon Crawl Classics explicitly includes equivalent spellcasting fumble rules but mostly because I think the alternative leads to some unfun playstyles pretty quickly

The general rules on the use of Action Dice don’t mention auto-fails on a Natural 1.

Action dice: Action dice are used to make attacks, use mutations, or execute wetware programs. The most common use of an action die is to attack; most characters roll 1d20 for their attack rolls because they have a 1d20 action die.

As characters advance in level, they may gain additional action dice. Typically, these start as additional dice of lower facings (i.e., a d14 instead of d20) to reflect that the character’s secondary attacks are not as effective as his primary attacks. Character classes with mutations or wetware pro-

gram use may be able to use action dice to make additional attacks, as described in the class descriptions.

Core Mechanic of Combat

THE CORE MECHANIC

The core mechanic in the Mutant Crawl Classics Role Playing Game is the d20 roll. You will frequently be asked to roll 1d20 and add or subtract modifiers. The goal is to roll high and beat a Difficulty Class, or DC. Sometimes the DC will have specific terms, such as an Armor Class, or AC, which

is a combat variety of a DC. A higher DC is more difficult to beat, and a better-armored creature has a higher AC.

If you roll equal to or higher than the DC (or AC), you succeed. Otherwise, you fail.

A roll of 1 is an automatic miss and often results in a fumbling failure of some kind.

A roll of 20 is an automatic hit and often results in a critical success of some kind.

Occasionally a character may roll a die other than 1d20 when acting. 1d16, 1d24, and even 1d30 are used for weak er or stronger character classes.

These are the specific rules on using mutations and mutation rolls

MAKING A MUTATION CHECK ROLL

For a base mutation check roll, the player rolls the appropriate action die (determined by genotype and class level) and adds their genotype’s class level to that die roll. For example, a 1st-level mutant would roll 1d20 (action die) + 1 (class level), and then compare the result to that particular mutation’s results chart to determine the effectiveness of the mutation’s use.

Any single mutation check roll can also be increased by either burning Luck or by employing glowburn, or both. Glowburn use must be announced before a mutation check roll is made, however, Luck use can be announced at any time including after the roll is made.

GLOWBURN

Beginning at 1st-level, a character may elect to use glowburn to increase a mutation check roll. Glowburn use must be announced in advance. To use glowburn, the character burns off points of physical abilities (Strength, Agility, or Stamina) and adds one point to the mutation check roll for every point burned off their abilities.

In play, this represents the mutant voluntarily ingesting any mildly radioactive material that the mutant has gathered up in his or her journeys for just this purpose – causing the mutant great pain and sickness as a side effect – but also briefly amplifying the effects of one mutation.

Glowburned abilities will heal back at the rate of one point per day that the mutant does not glowburn. Additionally, any glowburn that reduces an ability below a value of 3 requires complete bed rest and inactivity until that ability heals back to a value of 3 or above.

NOTE: Normally only mutants, manimals, and plantients are able to use the glowburn mechanic. The one exception to this is the shaman class for pure strain humans. Shamans also keep small collections of random radioactive detritus and sometimes swallow these to increase the efficacy of running a patron wetware program.

So that’s the Rules as Written and the Rules as Written as I understand them are.

Making a Mutation Check Roll

Mutant Crawl Classics rule book page 43. Roll the action dice, add bonuses and class level and compare *result* (not roll) to the mutation results chart. Luck burning and Glowburn modifiers can be applied.

Rules as written it’s impossible for a Level 1 or above character to have mutation *result* of 1 unless they have the Birth Sign Genomorph: Mutation Checks and a negative luck modifier.

It says nothing about natural 1 or natural 20. Not about them being an automatic failure or success or about them causing a fumble or a defect.

This contrasts with the Dungeon Crawl Classics rule book, (11^th Edition page 106) on the casting of spells which explicitly says:
Criticals and fumbles: A spell check result of a natural 20 is a critical success. The caster receives an additional bonus to their check equal to their caster level. Compare to the casting table for that specific spell for the result.

A spell check result of a natural 1 is always a failure. A result of 1 may also result in corruption or disapproval, as described below. (and later in the rule book are the multiple stages of turning a Spell casting Fumble into a misfire or corruption the Dungeon Crawl Classics equivalent of a Defect.) These are some of the guardrails I mentioned earlier. In Dungeon Crawl Classics spell casting, roll a Natural 1, then go through a process where you roll and roll again and make choices about accepting impacts before you end up with Corruption. Similarly, roll a Natural 1 in combat, get killed, you have a chance to be healed or have a comrade roll you over and found out you are still, just, alive.

So even in Dungeon Crawl Classics which has explicit rules for Fumbles in spellcasting you don’t automatically move to a corruption / defect. Corruption in Dungeon Crawl Classics is also more picturesque than Defects in Muant Crawl Classics. Some of those Muant Crawl Classics Defects are a walking death sentence. Or in the case of Devolved (on page 91) a non-walking death sentence.

So that’s RAW.

And I think RAW is very much rules as intended because applying a Defect on all mutation check rolls of a 1 is rapidly going to result in unviable characters. My interpretation is  supported by the game implications of a Natural 1 resulting in a defect. Defects in game are mechanically bad. They aren’t cosmetic or roleplay opportunities. They will break your character and not in a fun way. You are no longer playing to find out, you are playing to find out how your character died.

The probabilities work out at something like this.

If you are using a mutation 8 times a session you have a 90% chance of acquiring a Defect in 6 sessions. 10 sessions give you 90% chance of having 2 Defects. Your chance of reaching 20 sessions with zero defects at 8 rolls a session is 0.03%. Over a medium-length campaign, most mutant characters are likely to accumulate multiple serious defects.

An example from play. My character in Mutant Crawl Classics has Cryokenises as a combat mutation. Average duration of combat 4 rounds. Average 2 combats per session. If she uses Cryokenises to hurl some ice daggers in every round of every combat that’s 8 uses per session. Add in some uses of a utility mutation twice per session for 10 total uses of mutations per session that is a 40% chance of triggering a Defect every session. For non-combat heavy sessions my character is going to be using Telepathy to negotiate or Telekinesis to solve special problems.

If you apply the folkrule in Mutant Crawl Classics that a Natural 1 on a Mutation Check causes a Defect there is a 40% chance per typical session that your character picks up a Defect. By the end of an adventuring month with 4 sessions covering a couple of days of in-game time each the chance of having 1 Defect are very high and the chances of having two are high.

Two defects makes your character hard to play – retiring the character levels of hard to play.

Some of those Defects have some pretty profound impacts. That doesn’t make them unplayable but it does significantly impact their viability. Two or more Defects start to make your character dead but walking.  That’s a significant detriment for using the very game feature the game is named for.

Rational Response to the Rules as Not Written.

So how do players adjust to a Mutation Defect Fumble rule. Rational player responses become, avoid mutation use, switch to Pure Strain Humans, retreat for extended periods after every defect, get hold of Molecular Integration, or optimise around Glowburn / luck recovery.

The Rules of Gaining Defects in Play

Rules as written have a couple of paths to gaining Defects in play

Radburn. Exposure to high levels of radiation may add or subtract mutations from a Mutant, manimal or plantient character Level-1 or higher. Whenever a character is forced to make a Fortitude Save vs radiation-based damage a result of a natural 1 causes the mutant etc to immediately lose 1 random mutation or defect. If the mutated character makes the required save by rolling a natural 20 the gain one random mutation or defect. Use the RadBurn Table 3-1

D20 Table

Defect on 1-2

Mutant Physical Mutation 3-13 Mental Mutation 14-20

Manimal Physical Mutation 3-15 Mental Mutation 16-20

Plantient Physical Mutation 3-20 Mental Mutation #NA

That’s the main route for Level 1+ Characters to gain defects. That and messing with specialist Artifacts. Which is an integral part of the game. Every Mutant Crawl Classics adventure I have played has some machine which will randomly give you a mutation or a defect if you fiddle with it. You are encouraged to fiddle with it. That is part of the fun.

Conclusion

I’m not opposed to mutation instability as a concept. I actually think it fits Mutant Crawl Classics very well but I think tying permanent Defects directly to natural 1s creates long-term incentives that work against the core gameplay loop of using mutations normally. I’d much rather see a system where instability escalates over time and creates weird side effects, misfires, manifestations and has a push-your luck mechanic which can trigger occasional serious consequences for over ambitious Player behaviour rather than immediate permanent degradation for Character behaviour.

Perhaps I should write such a sub-system for myself.

Appendix A – Unpacking the Probabilities

If a Natural 1 on a Mutation Use table triggers a defect then the number of sessions estimated to pick up one defect based on usage per session is

P(≥1)=1−(0.95)(rolls per session×sessions)

Rolls / Session	Sessions for 90% chance (≥1 defect)
3	15 sessions
4	12 sessions
5	9 sessions
6	8 sessions
7	7 sessions
8	6 sessions

Chance of picking up two defects from those usage patterns is

solve for:

This occurs when total expected defects ≈ 4, so:

Which simplifies to:

Results

Rolls / Session	Sessions for 90% chance (≥2 defects)
3	27 sessions
4	20 sessions
5	16 sessions
6	14 sessions
7	12 sessions
8	10 sessions

Chance of getting to 20 sessions zero defects

Results

Rolls / Session	Chance of 0 defects after 20 sessions
3 (60 rolls)	4.6%
4 (80 rolls)	1.6%
5 (100 rolls)	0.6%
6 (120 rolls)	0.2%
7 (140 rolls)	0.08%
8 (160 rolls)	0.03%

At typical usage (5–8 rolls/session), avoiding defects over 20 sessions would be very very lucky

Results: Chance of ≥4 Defects After 20 Sessions

Rolls / Session	Total Rolls	Expected Defects (λ)	Chance of ≥4 Defects
3	60	3.0	35%
4	80	4.0	57%
5	100	5.0	73%
6	120	6.0	85%
7	140	7.0	92%
8	160	8.0	96%

Modest usage during a short campaign probably leads to two defects. Moderate usage might easily lead to more defects than mutations and that situation continues to get worse.