While the diversity that comes with most parties are a source of much drama and enjoyment, restricting characters to a single class, race, background, deity, or other element can give rise to fun and unique campaigns. An all-elf party will tell a different story than an all-paladin group, even if they are playing the same adventure.
Regardless of the restriction applied, having a common thread between all characters allows the DM to involve all characters in the plot far easier than a normal party, and enables much deeper exploration of the themes and motifs of that character facet.
Even more than usual, character creation in these types of campaigns should be a coordinated effort among the whole group. Depending on the restrictions at play, players might struggle to fill the traditional roles in the party. Clever building and off-the-beaten-path options can sometimes alleviate this, but it might also require altering how the group tackles problems. Perhaps a head-on assault could work for the all-Fighter group, but the all-Bard party would struggle.
Thirteenth Warriors
These campaigns shine when every member of the party embraces the theme. While it might be tempting to have a single paladin supporting an all-glass-cannon wizard party, this runs the risk of turning the renegade character into the focus of the campaign, and makes it harder for the DM. The imbalances and imperfect groups are what makes this type of campaign fun, and you should play into the theme instead of trying to fight it!
Class
Perhaps the most obvious, but also one of the strictest, restriction is having all characters play the same class. Depending on the campaign, the DM might even restrict multiclassing in a mono-class campaign. When building a mono-class party, care should be taken that each party member still has a niche they excel at. For this reason, it is probably not a good idea to have characters with the same subclass, except for a few exceptions where the subclass offers multiple choices, such as the Battlemaster Fighter.
Wizard
The arcane cabal of wizards is a classic archetype, and makes for a open player-driven campaign. Knowledge and research will be paramount to the success of an all-wizard team, who are almost unstoppable when they know what the next adventure brings and prepare accordingly.
An alternative to the seasoned wizards are the apprentices in magic school, a campaign that could take place over multiple years, as a series of smaller adventures.
Rogue
A guild of thieves, a ring of spies or assassins, or a detective agency are all possible ways to run the all-rogue party. As with the wizards, preparation and intelligence-gathering will be the name of the game. Heists, and the preparation leading up to them, are the bread and butter of this type of campaign. Any job which requires a special crew likely also needs special equipment, perhaps stolen in a series of smaller preparatory heists.
Without access to magical healing, the rogues will have to be precise in their planning and execution, striking from the shadows with the element of surprise. It is possible to build rogues who specialize in any of the mental stats, which provides an interesting difference between party members.
Paladin
Chivalric orders are rife with opportunity for adventure. Will the paladins prevail despite horrible odds, saving the innocent at great cost to themselves, or will they fail to fulfill their holy vows? Perhaps they have been entrusted with a mission from a deity to find an artifact, or to protect a dangerous secret from those who seek it for evil?
Another fun take on this campaign is to play as the founders of an order, who have to make a place for themselves in the world.
Cleric
The all-cleric party comes in two distinct flavors. The first is the monotheistic party, where everyone is a cleric in service of the same deity, perhaps as Charitors of the Pilgrim Knights under Freya, or as prophesized champions of Odin. It is still possible to play as different domains, representing different aspects of the same deity.
The alternative is a polytheistic campaign, where some threat forces followers of multiple gods, perhaps ones normally diametrically opposed, to work together. Regardless, an all-cleric party explores the philosophy of divinity, and the power of faith.
Bard
The band is getting back together! A group of entertainers who specialize in different instruments or performances makes for a very social campaign. Who is playing the drums, and who is on vocals? Is there a talent show to win, or are you on tour to earn enough money to live the rock'n'roll lifestyle forever?
Since bards are learned spellcasters, could do a snake draft of spells to differentiate the characters.
Warlock
The warlock presents a special case due to their extreme customizability. It is possible to play a coven of warlocks in service of the same entity, and all pick the same subclass. The characters are instead differentiated by their invocations, spell choices, and pact boon choices.
Is the party trying to bring their Fiend patron to the material plane in a magical ritual? Are they the heralds of an elemental invasion, serving a court of Genies?
Race
Playing a mono-race party is a great way to have a common motivation. Maybe the party all hail from a single settlement, or are members of a militia unit? Maybe the party are all related, and have come together to for a family funeral, religious feast, or other occasion? The mono-race party is less restrictive than the mono-class party, and much of the normal party building advice applies.
Any all-race campaign is a deep dive into a particular culture, ripe with opportunity for meaningful relationships and grounded stakes.
Monstrous races
A group of all monstrous races could be a fun way to play an evil campaign - or subvert it. Perhaps the party are a raiding band of orcs or goblins who are enemies of the civilized world, or they are just trying to survive on the edge of society and have to fight off adventurers trying to invade their cave.
Maybe, they are the Dhampir spawn of a vampire lord, each vying for their master's favor in plotting within and between different vampire clans.
Elves
An all-elf party could be a squad of Wardens, recruited from the populace of Iacaris and given an important task for the Kingdom, and latitude to carry it out in whatever manner they see fit. Perhaps they are all scions of a princely house of Amnora, seeking to navigate the social jungle and further their own purposes.
Sylvanites
A party consisting only of the Feywild-connected races, such as Tabaxi, Ursinians, and Aquilon sets up a fun and whimsy campaign focused on the oddities of the fey lands under the eternal stars, or the politics of Ancalos.
Dragonborn
An all-dragonborn party could be the children of a single broodmother, or wards collected from various roosts in order to keep a fragile web of alliances intact. Regardless, this campaign could explore the dragon war, from either side.
Background
The mono-background party can either be members of a faction, or all connected through a single event that took place before the campaign started or during the first session. This is one of the easiest restrictions to build around, and mostly serves as a theme for the campaign. Some backgrounds, such as Entertainer, almost works as "class-lite", letting the campaign center on themes of a class without specifically mono-classing.
Some background-based campaigns might have this be the only part of the backstory that matters. Of course, having an idea of who your character is beyond the restriction should inspire your roleplaying, but might not come up during the game, making this style of campaign well suited to oneshots or shorter campaigns.
Sometimes, the mono-background also comes with a natural group patron, such as the commanding officer of a unit of Soldiers, or the captain of a Pirate ship. The organization-based backgrounds are an opportunity to explore that faction deeper, perhaps climbing the ranks until the party are the ones in charge?
Examples:
- A guild of Artisans have to put their skills together to complete a major project.
- A unit of Soldiers get lost behind enemy lines and have to make it home.
- A crew of Sailors on a ship get shipwrecked on a mysterious island.
- An expedition of Archaeologists on a mission to explore a lost ruin.
- A family of Nobles are knee-deep in a conflict with another family.
- A tribe of Outlander nomads have to traverse a dangerous desert.
- A street gang of Wayfarers protect their alleys from rivals while trying to get away from poverty.
- Courtiers engaging in political intrigue with a rival polity.
- A troupe of Entertainers touring the islands to put on shows.
- A watch of Guards have to track down a serial killer.
- A caravan of Merchants must protect their valuable cargo in the wilderness.
- Two Criminal gangs join forces for a complicated multi-step heist.
Deity
Not to be confused with the all-cleric party, the mono-deity party simply believe in the same ideals. This usually comes with similar alignments as well, which allows the campaign to explore the cosmic conflict across the multiverse.
Examples:
- A squad of Pilgrim Knights in the service of Freya.
- Black Maidens who carry out Hel's will on the material plane.
- Cultists of Loki, seeking artifacts of their deity.
Wildcard
An idea which might work best in a shorter, less serious, campaign is to determine all characters with the help of the dice. Everyone rolls for class, race, stats, personality, and HP. A discussion would have to take place how far this should go - what about subclasses, spell selections, and feats? Perhaps the rolling could even take place during the first adventure, with the characters emerging with the narrative?
This would be highly chaotic, but it could be fun to explore a character you would not build normally.