One offs are taxing on the DM. Whether you're introducing new players or squeezing in a game with friends too busy for a lengthy campaign, you end up putting a lot of work into a single session. The pressure to impress can be exhausting and the amount of work unrewarding. By simplifying the game mechanics and leaving yourself room for improvisation, you will have a better, more fun game.
Kyle's Rules for Managing a One Off
Present classes as professions. Players cracking open any edition for the first time will be met with pictures selling the classes to them through cool looks and abilities. New players, particularly video gamers, will gravitate toward something they deem cool, matching flavor or fighting styles they've seen in the past. Likewise, roleplayers might consider taking on outrageous features to make their characters more interesting only to find 10 minutes into the game they can't sustain the façade of a wise cracking gumshoe or adventurer historian. Instead, begin your character creation by explaining the world they inhabit. Ask them to pick a profession with a description of what their daily lives are like. From this, give them a single class feature that sets them apart without dictating their playstyle. An innkeeper might have a rogue's sneak attack from years of weapons held under the bar. The local physician might have the amazing ability to cure the sick in a flash of holy light. Some other options might include:
A class ability, like sneak attack, smite evil, barbarian rage or turn undead.
A class feature, like animal companion, unarmed attacks, favored enemy, familiar or detect evil.
A feat, like power attack, two weapon fight, improved grapple, mounted combat or rapid reload.
A level appropriate spell from the cleric, druid, sorcerer or wizard list.
Humans only. With limited time, players will struggle to imagine their party members as fantastical races, like dwarfs, elves and tieflings.
Simplify stat creation. When it comes to basic stats, the quickest way to make a character is to give them preset numbers to place where they choose.
One off characters need to hit their targets in combat to have fun, however some missing can provide great tension. Help newer players place their stats appropriately, and read out the modifiers when everyone is ready.
Give everyone eight skill points to spend. Don’t worry about class skills and cross-class skills. As long as nobody raises a stat above four plus their level, things won't get imbalanced. Characters that won't be leveling don't need complex risk/reward min/max systems.
Give everyone 1d8 of health. This is for the players’ benefit as much as yours. Lightly armored characters will be more resilient to their mistakes while you have an instant frame of reference for all the damage you dish out—4 is a mighty blow that would kill a normal person; 1 is a battle injury.
Assign simple weapons and armor. Weapons and armor are an integral part of establishing the look and feel of a character. In your world, certain professions would likely use certain weapons or have access to certain types of armor. Ask the player what they would carry on their person and what they would keep at home. To keep this balanced, if you use an enemy from the Monster Manual, use weapons and armor from the Player’s Handbook. Give players free reign to choose as long as it does not inhibit the story.
Use starting items. Give players the starting packages from the game book. Half these things are flavor oriented, like a bedroll and candlesticks. Take advantage of things like arrows and bolts to add a dash of realism to your campaign’s outset.
Start with a day in the life. Open the game by going around the group asking what their characters’ daily schedules are like. Let them each have unique but relatable experiences. When they finish, work into their story a place where they regularly gather. Whether it’s the local tavern, shrine or great hall, give each player a chance to develop how they got there and what their day was like up to that point.
Draw the map as you go. As your players describe themselves, give them an idea of the town they live in and let them add where they live in it. Give them roads and what lies down each direction. Place any essential buildings for your plot and allow group storytelling to establish the rest.
Let information come from three sources. To achieve an immersive story in a short amount of time, you need to introduce players to the lore slowly. Make unraveling the quest part of the puzzle. The first piece should come from a reputable source, either a character or guild the PCs would encounter on an average day. The second source should be an outsider, be it someone that has seen something otherworldly or has tales to share from a foreign land. The third should come from authority, whether by divine happenstance or from a dying quest giver.
Run a trial encounter close to home. Give the players a chance to experiment with their abilities. End it by giving them a clue to the greater adventure ahead. This can be as simple as a fight with lackeys that obviously belong to a specific creature type or a seemingly unrelated challenge that gets the players noticed.
Solve a problem close to home. Let them see exactly how the threat will affect their lives. This may be combined with the previous encounter or be part of an entirely new one. Encountering a nearby burned down village could teach players more about a rogue fire elemental than another combat encounter.
Travel to the boss arena. By this point, you are probably three hours in. It’s time for a change of scenery to establish the end of the adventure. Boss fights should be well planned out and take advantage of the mechanics the characters used over the course of the game. By making this a new location, you can protect it from being activated prematurely.
The once profitable logging hamlet of Timberspine has fallen into disrepair, its meager remaining wealth squandered on the residing governor’s unfinished keep. While the townsfolk toil, he stays locked away, scheming to return his charge to its former glory. To that end, he commissioned a great golden idol be crafted to adorn the town’s church to bring in worshipers from far and wide. Word has spread of its majesty, even reaching the ears of Neferrot, a black dragon residing in the muddy springs of the mountains to the north. Unable to resist adding the glistening idol to her collection, Neferrot has taken wing, speeding toward the town under the cover of night.
The Bug Eye’d Dog Tavern has several of its usuals that night. Seamus Scroggs complains in his customary rhetoric about the governor overtaxing his farm. Ignis Petti is spouting her usual nonsense, having seen a great flying beast through her old, clouded eyes. The only thing different is Frank Dorn’s demeanor. Normally one of smug authority, he sits shaken, nervously counting his earnings behind the counter. Earlier that evening, three knights arrived, two wounded and one barely breathing, all covered in horrible blisters and burns. Having paid double for his silence, they took his largest room and haven't come downstairs since.
A sudden tremor fills the inn with the clatter of pewter. The two knights still in their tabards and armor come racing downstairs. Informing the patrons to stay inside, they throw open the door and rush out. A great jet of green rolling bile comes careening down the street, plowing them over as it melts skin from bone, covering the windows. At the sight of this horror, Frank leaps over the bar and slams the door shut as a thunderous roar rings out. The deafening clatter of splitting wood and breaking stone echoes from across the street. As the cacophony fades with the beat of heavy wings, the streets return to silence, soon followed by a rhythmic knock on the front door joined by one from the upstairs room.
Reduced to bones and blistered metal, the knights have heard the call of their new master and rise from death. The heroes, whether by necessity or sense of righteousness, defend the town. In the aftermath, the church across the street lies in ruins, its great idol missing and its keeper dying outside. His final breaths inform the players of a legendary sword hidden beneath the altar. All too late, the governor sounds the keep’s alarm bell, rallying his paltry troops to his defense. Eager to remove the problem he invited on his town, the governor hires the players to set out for the mountains to the north.