Caveat: Very little about Dungeons & Dragons is intended to be clear cut. There are literally dozens or even hundreds of interpretations of how any particular mechanic works to simulate the real world or something else, etc. This is mine. YMMV.
Critical Hits and Fumbles
Most gamers agree on what should happen when you roll a natural 20 on an attack roll: an automatic hit that does extra damage, representing a super lucky shot. We might disagree on the particulars (double damage? Max normal damage plus a bonus? Roll to confirm? Etc) but we all tend to agree it’s a good thing.
What about a Natural 1, though?
What is a Natural 1?
A Natural 1 is just that–you roll a d20 and roll a 1. That’s a 5% chance and is commonly understood to represent a stroke of rotten luck. The game defines a Natural 1 on an attack roll as an automatic miss, no matter how ideal your situation was or how easy it was to hit the target, short of an automatic hit.
But should something else happen in addition to a miss?
There’s endless debate about what should happen with Natural 1s, and a whole cottage industry of people putting out tables, house rules, and even 40-50 cars decks of “critical fumbles,” where if you roll a 1, you draw a card and follow the doom specified thereupon.
And to an extent, that’s what I’m doing here, but I want to talk about another aspect one should be considering: the relative rate at which different characters will be rolling Natural 1s.
Specifically, the more attacks you have, statistically the more often you will roll a 1.
Credit: Invisible Citadel
Better Fighters Screw Up More Often?
Say you’re a high level fighter. You’re a master of your craft and a legendary terror with your chosen weapon. Most foes quake in their boots to hit you, and you almost always hit your target–you might need to roll only a 5 or higher to hit almost anything, say. And you attack 4 times during your attack! Amazing!
But your chances of rolling a Natural 1 and screwing up are the same as everyone else: 5%
If you have multiple attacks, though, each of those attacks has a 5% chance of a Natural 1. Now, I’m not a statistician, but the odds of having rolled at least one Natural 1 over the course of a combat when you’re rolling 4 times with each attack action are a bit higher than a mere 5%. Your typical level 1 fighter is statistically 100% likely to roll a Natural 1 in a twenty round fight (having made 20 attacks), but a 20th level fighter making 4 attacks a round is statistically 100% likely to roll a Natural 1 in a five round fight, and four Natural 1s over the course of a twenty round fight.
See what I mean?
To make matters more specific, the most common results of a Natural 1 that people use are 1) you hit yourself or an ally with the attack, doing either normal or a lessened amount of damage, and/or 2) you disarm yourself or break your weapon.
Now, I’ve occasionally heard people scoff at the very idea of a high level fighter breaking their weapon or being disarmed, and I want to push back on that a little. It’s easy, in the wild chaos of combat, to have your weapon jostled from your hand–say your hand is slammed against a wall and you lose your grip, or the hilt is slaked in green ichor, or whatever–and weapons are not as tough as we all think. Swords break and bend and grow dull all the time, especially if they’re used for a long time.
But consider, though, the odds of your high level fighter losing their weapon in a given round, which are much higher than any other character. Or that same fighter being disarmed multiple times in the same round.
Does that make sense? Not really.
I prefer to think of a natural 1 as the game reminding you to introduce some cool and unexpected event to keep things fresh and surprising. Remember the point is to keep the action fun and exciting for the players.
Cypher does this: when a player rolls a Natural 1, it prompts a cost-free GM Intrusion, where the GM has a new event happen (normally they have to give the player XP to great an intrusion). And it works pretty well there. (I like to give players XP anyway, as it encourages them not to spend XP to reroll but to embrace failure as a means of learning in the game.)
Here’s a list of “interesting things” that can happen when someone rolls a natural 1. Most are negative, some indirect, some even positive. Ignore or reroll events you don’t like, or make up your own thing that works in the situation.
Natural 1 Table
When anyone rolls a natural 1 on a d20, roll d10 and consult the following:
Enemy reinforcements show up (no more than 1/4 the original CR, such as 1-2 more goblins to aid a warparty of 6-8 goblins). If you get this result again, roll again–reinforcements should only appear once per combat.
The attacker inadvertently hits themselves; attacker takes half damage from the attack.
The attacker leaves an opening that can be exploited; next attack against them before the start of their next turn has advantage.
The attacker slams their weapon against a shield, thick hide, or other firm surface, jarring it from their hand; attacker is disarmed.
The attacker over-extends, over-reaches, and/or slips and falls; attacker knocked prone.
The weather radically changes (if outside), an earthquake/cave-in starts shaking everything (if underground), etc. This can have any number of effects on the battlefield, such as requiring Dexterity checks to remain standing, inflicting disadvantage on attack rolls, etc.
The target gets a second wind; restore 2d8 hit points to the target. (See my post about Hit Points for more on this topic.)
The attacker recovers from their swing into a defensive posture; the next attack against the attacker before the start of their next turn has disadvantage.
The attacker drives back the target with a wild swing and gets an unexpected break; restore 2d8 hit points to the attacker. (See my post about Hit Points for more on this topic.)
The character spots a weakness/armor gap/opening in the enemy they attacked, granting advantage on their next attack against that enemy before the end of their next turn.
You could certainly substitute your own events or add to this chart, making it a d20 roll or even a percentage roll for a random event from a massive list. The point is to have fun with it and use Natural 1s as an opportunity to make things more interesting for your game.
Tl;dr: Straight up “you miss” is less interesting than “you miss AND…”