When your players get a natural 1 on their dice rolls, what do you as a Dungeon Master/Game Master do or say? What's your technique? I know that largely it depends on the situation (ability checks vs saving throws vs combat etc) in most cases, as for what happens specifically - but I'm talking in general terms. Is it simply a failure per the original rules as written in 5E? Or do you go with the variant rule where 1's are treated as Critical Failures? In either case, or a case I haven't presented here - how does that work mechanically in your game? I'm now going to make the case to you for using natural 1's as Critical Failures and also adding a touch of the unexpected to simulate the randomness of everyday unlucky moments.
*This was made with D&D in mind, but you can easily use these techniques for any games where the crit system is represented by a low roll or natural 1.
How Competent Are the Characters?
When I think about what happens with a botched dice roll, often I'm thinking about several different factors when I'm trying to decide on the fly what sorts of penalties or consequences I will impose as a DM/GM for a natural 1. One of the biggest factors I think about is how competent the characters are, and what level they are or whether they're attempting to do something outside of their normal skillset. The reason for this is simple - I find it easier to believe that a level 1-5 character will do something stupid like drop their weapon in battle, or accidentally shoot their teammate, or possess equipment so shoddy that the sword blade snaps in the middle of a hectic fight. Levels 6-10 I generally would have to think of something more creative for botched rolls, such as environmental factors, or possibly just giving the enemy advantage on their next attack against that character due to an exploited weakness, or maybe even reinforcements showing up for the bad guys. So, if I wanted a character to fall on the ground by accident (tripped, etc), that may be applicable for levels 1-5 but maybe 6-10 I'd have the BBEG actively kick the player onto their back, or something in that same vein. A good DM/GM should know their players and their characters pretty thoroughly, so this shouldn't be too difficult for most DMs/GMs to dissect.
What's the Context?
Another major factor in determining what should happen when a player rolls a natural 1 is simply to ask yourself what's going on, and what's the context for their failure? Are they currently fighting frost giants in the middle of a raging snowstorm? Are they riding on giant ravens trying to speed away from an angry ancient blue dragon? Try to look outside of what they're actually participating in, and see what sorts of disadvantages might occur from that. For example, the natural 1 may have happened on a regular attack roll on the giants. The initial reaction might be to have the player simply miss their attack, or if you use the alternative rules - maybe they drop their weapon. However, with the environmental factors, you could factor those in and come up with even more creative ways for the player's character to epically fail. Maybe they get snow in their eyes (they miss the attack, and then get disadvantage next turn), maybe their hand gets so cold the weapon drops from their stiff fingers (they must use their entire movement next turn to search around in the snow for the weapon), or maybe they slip on some ice just underneath the snow's surface (they are now prone and must use an entire action to get up and away from the ice).
Don't Be Repetitive
The most important thing to remember, in my opinion, is to try not to be repetitive in which consequences you go with. Especially if you're being generic and not trying to come up with creative ways in which a character might fumble. The players will grow tired of always accidentally hitting their teammates or accidentally tripping during battle, or accidentally breaking their nonmagical weapons. Try to give your natural 1's some variety. With that in mind, I am going to drop some tables for random events below.
D8 - Melee Combat Fumbles
1 - The character's weapon breaks; either the handle snaps or the blade shatters or some other complete destruction of the weapon happens. (The character no longer has the weapon. Ignore result for magical weapons)
2 - The enemy disarms the character. (The enemy now has possession of the character's weapon. Magical items still must be attuned for them to be used, but it can still be used as a basic weapon in the hands of the enemy)
3 - The character accidentally drops their weapon, either from the shock of the hit, or from an inexperienced grip, or some other factor. (Enemy may make a free attack on you as a reaction with advantage, and the character must expend all movement next turn to scramble and pick up their weapon if they want it back)
4 - The character's weapon becomes lodged in a shield, enemy's armor, tree, or some other object during a wild and ferocious swing. (The character must make a DC 15 STR check to dislodge it)
5 - The character stumbles over a body, stray debris, some roots, or some other obstacle and falls to the ground. (The character is now prone, and the enemy has advantage on attacks)
6 - The character pulls a muscle during the attack, causing them to cry out in pain. (The character now has disadvantage on attacks and damage is halved until healed)
7 - The character gets something in their eye, such as a stray bit of metal or dirt or debris, as they swing their weapon around wildly. (The character gets disadvantage on all attack rolls for 1d4 turns)
8 - The character misses the enemy wildly and accidentally strikes a nearby friendly character or NPC. (Roll an attack using the friendly character's AC score, and then roll damage accordingly. If there are no nearby friendly characters then ignore this result.)
That's just a basic random table for critical fumbles that you can use for inspiration. If this post ends up being popular, I'm guessing we may do a more advanced and detailed table for melee fumbles, ranged fumbles, spell fumbles, and the like. Let us know what you think, and may your players curse your name when you make them lodge their magic sword in the trunk of a tree. - Joe