A one-shot is the hardest kind of game to prep for, because you need a whole small world for one evening and none of it will be reused. The trick is to spend your prep time on the parts players will actually remember, which are the people and the moments of danger, and let random tools fill in the rest. This guide preps and runs a four-player, three-and-a-half-hour one-shot with three of the site’s tools: the character generator for the villain and the quest-giver, the NPC generator for the town, and the dice roller at the table. It also covers where each tool stops, because two of them repeat themselves more than you’d guess.
The example adventure is a festival in a river town where lanterns keep going out and people keep going missing. Four level-3 characters, one evening, about 45 minutes of prep.
Step one: the two characters the story hangs on (15 minutes)
Start with the Random Character Generator. Each click of Generate a character draws a species, a personality trait, a quirk and a name from pools of 30, 30, 30 and 35, which is 945,000 combinations. It was built for artists and writers rather than for D&D specifically, which is useful here. A trait like “Secretly soft-hearted” or “Keeps a running tally of favors owed” is a motive, and motives are exactly what a one-shot villain needs and a stat block doesn’t give you.
Roll until you have two keepers: the antagonist and the person who hires the party. A good pairing is one where the traits pull against each other. If the villain comes out “Coldly logical” and the quest-giver “Hopelessly romantic”, you already have a scene where the quest-giver begs the party to spare someone the villain sees only as a variable.
The species pool goes beyond a fantasy setting. Five of the 30 (Robot, Cyborg, Android, Alien and Time traveler) won’t fit most tables, so about one roll in six lands outside the genre. Reroll those, or reinterpret: an “Android” in a river town is a clockwork servant someone built and abandoned, and “Clockwork automaton” is already in the list. Treat the result as a prompt, as the tool’s own instructions say, not as a finished character.
Tick No repeated characters if you prep several games from the same browser. It remembers full combinations and rerolls an exact repeat, but it only compares the whole combination. Names and species can still recur from one roll to the next: with six rolls, the chance that two share a name is 36%, and that two share a species is 41%.
Step two: stock the town (15 minutes)
Players will talk to more people than you planned. The Random D&D NPC Generator is built for that: one click of Roll NPC gives a name, a race, a class, a voice and a quirk. There are no filters to set. The voice is the part that pays off at the table, because “clipped” or “warm and slow” tells you how to say the line, not just what to say.
Roll ten before the session, one for each role you can predict: the innkeeper, the festival organiser, a guard, a lantern-seller, a rival adventurer, and five spares for whoever the players decide to interrogate. Then edit them, because ten draws from these pools almost always collide.
| Ten NPCs rolled from the generator’s pools | Chance of at least one repeat |
|---|---|
| Same name (26 names) | 86% |
| Same quirk (15 quirks) | 98% |
| Same race (12 races) | 99.6% |
Repeated races are fine; a river town full of humans and halflings is plausible. Repeated names and quirks are not, because the players will notice when two people “carry a single die in a pouch”. Rename one of each duplicate pair and swap the quirk for one of your own. The generator has no no-repeat option, so this edit is part of the job, not a sign that something went wrong.
The Recent results panel holds the last ten results in your browser, which happens to be exactly the size of this cast. It’s handy as a crib sheet, but the eleventh roll pushes the first one out, so copy the ten into your notes before you roll any extras. Export CSV saves only the result on screen, not the whole list.
Step three: build the encounter table yourself (10 minutes)
The NPC generator only makes people; it doesn’t build monster encounters. For those, write a short table and roll on it with the Random Dice Roller, which gives you any of d4, d6, d8, d10, d12, d20 or d100, a custom die from 2 sides up, up to 20 dice at once and a flat modifier. Every die shows separately as well as the total, which matters in a minute.
For the walk along the river to the old mill, use the classic structure: three checks along the way, and an encounter happens on a 1 on a d6. The chance of at least one encounter on the trip is 1 − (5/6)³, about 42%, and with four checks it would be about 52%. If you want the encounter to happen, don’t roll for it; just have it happen. A random check is for when you genuinely don’t mind either way.
When it does happen, roll a d8 on your table and 2d4 for how many creatures show up:
| 2d4 total | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
|---|---|---|---|---|---|---|---|
| Chance | 6.3% | 12.5% | 18.8% | 25.0% | 18.8% | 12.5% | 6.3% |
That bell shape is why 2d4 beats a d8 for a group size: five creatures is four times as likely as two or eight, so the encounter is usually the size you balanced it for. If you only put a dangerous entry in slot 8 of the d8 table, there’s a 1 in 8 chance per encounter of meeting it, and across three encounters that becomes a 33% chance of meeting it at least once. Settle on one in three as acceptable before it goes on the table, or move it.
Step four: at the table
Use the dice roller for the rolls you make behind the screen. Three habits make it more useful than it first looks.
Advantage with two d20s. The tool rolls one die type at a time and adds them up, so there’s no advantage setting. Roll two d20 instead and read the two chips, taking the higher one. Set the modifier to 0 for this. The modifier is added to the sum of all the dice, so with two d20s and a +4 the big total number is meaningless; add the +4 to the chip you keep. The difference advantage makes is large. Needing 15 or better, a single d20 succeeds 30% of the time, advantage 51%, and disadvantage only 9%.
Big damage in one click. The villain’s fireball is 8d6: set the die to d6, the count to 8 and click Roll the dice. The average is 28, and the result lands between 22 and 34 about 82% of the time. The tails are equal, as you’d expect: 35 or more happens 9.1% of the time, and 21 or less also 9.1%. If 35 would down your wizard, that’s roughly one cast in eleven. Know that before the villain casts it, not after.
A record you can check. The last ten rolls stay under Recent results. When a player asks what the goblin rolled two turns ago, it’s there.
For odd dice, use the Custom option: a d3 for “which of the three missing townsfolk is still alive”, or a d2 if you’d rather not flip a coin.
Step five: improvising the people you didn’t prep
Players will ask the name of the guard’s sister. Keep the NPC generator open in a tab during play and roll once when it happens. Read the voice out loud straight away; committing to “plummy” or “nasal” in the first sentence is what makes a throwaway character feel planned. If you roll a name you’ve already used tonight, roll again; with six unprepared NPCs over an evening, there’s a 46% chance two of them would share a name from the 26 available.
The same goes for a surprise villain lieutenant. One click of the character generator gives you a trait to play, and a trait is all an improvised character needs for one scene.
The prep sheet, in order
- Character generator: villain and quest-giver, with traits that pull against each other. Reroll or reinterpret the out-of-genre species.
- NPC generator: ten townsfolk. Rename duplicates, replace repeated quirks, copy the list out before rolling more.
- Write a d8 encounter table and decide where the dangerous entry sits.
- Dice roller open in a tab: two d20s with no modifier for advantage, the villain’s damage dice set up in advance.
That’s about 45 minutes for an evening’s worth of people and danger. If you want more on any one tool, the post on rolling NPCs is about bringing a single generated character to life, and the post on dice math explains why 1d20 is flat and 2d6 isn’t. This one is about getting all three to carry a whole evening.