Dungeons & Dragons started with slightly different rules for monsters and player characters. In the dungeon, doors that players left open always swung shut, but “doors will automatically open for monsters, unless they are held shut.” Mostly though, the same rules applied to heroes and monsters, a carryover from the game’s wargame roots. In the wargames that led to D&D, players competed to win, while the game master—the referee—just interpreted the rules. Even in early D&D games, players sometimes battled each other in the race for treasure.

By D&D’s third edition, the game’s symmetry reached a peak. The game rules served as the physics of the game world. A monster’s statistics built from the same rules that applied to player characters. By sharing a rules foundation for characters and creatures, the third edition opened customization options like feats and class levels to monsters.

More recent editions loosen this symmetry, so monsters no longer work like characters. Why should they? Monsters serve a different purpose and rarely survive longer than five rounds. Nonetheless, characters and non-player characters follow identical game physics of d20 tests and DCs during play.

But some roleplaying games break this symmetry so that for non-player characters, the game master makes different rolls or no rolls.

Players enjoy rolling dice. In D&D, that makes attacking more fun than casting spells like sacred flame where the DM gets to roll a save. Rules like the Cypher System used by Numenera and The Black Hack variant of original D&D have players roll to determine the outcome both when they attack and when they get attacked. Monsters skip attack rolls in favor of players making defense rolls to avoid hits. Some games feature even bigger differences between the mechanics for players and game masters. In the Daggerheart roleplaying game, monsters attack with a simple d20 roll instead of the more complicated 2d12 Duality roll reserved for players. Only player rolls produce Hope and Fear.

D&D’s symmetrical system of saving throws and attack rolls has proved too entrenched to swap monster attacks for defense checks. But some symmetry in the game seems more ready for elimination. Start with contests.

In my ten years playing hundreds of fifth edition games, I played exactly one contest. It came when an intellect devourer did its thing: “The intellect devourer initiates an Intelligence contest with an incapacitated humanoid.” A few other monsters like nothics and poltergeists also start contents. Why don’t these creatures’ targets just make saving throws instead? Sure, the numbers work a bit differently, especially because contests can skip proficiency or use different proficiencies, but usually when players try to avoid harm, they just roll saves. The fifth edition design typically favors consistency over fussy exceptions.

Despite the rarity of contests, characters match their abilities against monsters’ abilities all the time. Mainly, the rules distill common match ups to a single check. This simplification comes most often when a creature hides. “The DM compares the Dexterity (Stealth) checks of anyone hiding with the passive Wisdom (Perception) score of each creature on the opposing side.” Instead of rolling both abilities in a contest, the check’s DC comes from adding 10 to a Wisdom (Perception) modifier.

This D&D rule benefits from a change that adds a dash of asymmetry so that players always make these checks. Players like to roll dice, especially when the roll decides their character’s fate. If a PC hides, the player rolls a Dexterity (Stealth) check against a DC set by the monster’s perception; if a monster hides, the player rolls a Wisdom (Perception) check against a DC set by the monster’s stealth plus 10. Tales of the Valiant takes this approach. Monsters get stealth and perception DCs for players to roll against.

D&D includes lots of creatures proficient in Stealth. When these creatures can ambush, they show the traits that make them more interesting than a claw/claw/bite sequence. When monsters attempt to ambush a party, the stealth DC toolkit works. Set a DC based on the ambusher’s stealth score and add a +5 to account for the advantage of advanced preparation. When the time comes for the monsters to spring, have all the players roll Wisdom (Perception) checks. Those who succeed avoid becoming surprised.

The technique of adding 10 to a modifier to set a DC can replace any contest. Players always roll and their opposition always sets the DC. If the opposition has advantage or disadvantage, modify the DC by another +5 or -5.

Contests offer different odds than ordinary checks. A contest’s two dice gives bigger swings in the range of outcomes. So, with lucky rolls, a creature with no bonus can win a contest against someone with a +11 modifier. When that +11 adds up to a DC 21, a check with no bonus always fails. How often does such a large mismatch appear in play?

Also, the average roll on a d20 is 10.5 rather than 10 and rolls that tie the DC go to the person rolling. Both these factors give a little edge to roller, improving their odds in an even match. But D&D plays at kitchen tables rather than at casino tables. In play, a 1-in-20 edge and a rounding error that adds 2.5% hardly matters. Also, we could adjust the DC to offset the edge or ignore it. When players make the rolls and gain the edge, they have no reason to quibble.