Random Encounters and wandering monsters may seem like interchangeable terms, but they aren’t. They’re different concepts with different purposes and means of handling them, and have been for more than 50 years.

Wandering Monsters

Wandering monsters are encountered indoors. The idea is that the heroes shouldn’t be allowed to lollygag, searching every room and corridor, playing with strange things you put there, talking to weird NPCs you invented. They should be interrupted at some point by a monster who probably feels like they’ve intruded upon the creature’s territory or look delicious.

However, some creatures should be neutral or even friendly, if approached amiably. These interactions may be played as reaction rolls or, more likely, pre-determined as part of the adventure. Such encounters should be written into the adventure and not randomly plucked from a table of creatures found in dungeons.

A wandering monster check should be made every thirty minutes in a dungeon or so. It could be more often, if it’s a well-populated castle, or less often, if it’s a lonely crypt. Traditionally, it happens on a 1 on a 1d6, but you could also use a countdown timer to make sure it happens eventually.

Random Encounters

Random encounters occur outdoors (or in some vast underground “wilderness”). The idea is that heroes can’t traipse thru a forest, marsh, or moorland without consequence. If they live in a dangerous world, they should encounter dangerous creatures.

But a random encounter should have a good chance to be non-hostile. Use reaction rolls to determine if the creature is hostile, wary, curious, or amiable. Beasts will have simple reactions, but NPCs and intelligent monsters can be approached with care and purpose for complex interactions.

It’s best if the creatures encountered are mostly part of the adventure and not always just random creatures appropriate for the terrain. They may not be directly tied to the main opponents of the adventure, but they could be part of a sub-plot of their own. And they should be appropriately thematic.

• If the adventure features a vampire or necromancer, then werewolves and giant bats are appropriate, because the bad guy probably lives in a creepy forest or on a spooky moor.
• If it features nobles, elves, and druids in a dispute over a wild forest, then fae creatures might be appropriate.

Random encounter checks may be made once per day or more, depending on how well populated the area is.

Morale Rolls

A significant part of all encounters—and random encounters in particular—is that most creatures have a morale score that can be failed, at which point they flee or surrender. Most creatures that aren’t undead or constructs (and even some that are) should be willing to run away so they can fight another day.

Old-school D&D gave a morale score in the stat block. If you play a system that doesn’t have it, just assign a score between 5 and 10, depending on how fierce and determined you judge the creature to be. If you roll higher on a 2d6 morale check, the creature looks for a way out: calling for an end to the fight, fleeing, or surrendering.

Check morale…

• When the creature is first encountered, if it was at least somewhat surprised and not expecting a challenge (not hunting or patrolling, for example).
  • This particularly applies to random encounters with natural beasts that aren’t especially territorial. Deer, for example, will almost always flee immediately; even bears can be scared off pretty easily if they aren’t hunting, protecting young, etc.
  • Since wandering monsters are always expecting a challenge when roaming a dungeon that contains other creatures, this doesn’t apply to them.
• After the first death among the creatures in combat (if several) or when it’s lost half its hit points (if alone or in a pair).
• When half the creatures (if several) have been killed or incapacitated (especially by magic) or (if alone or in a pair) if it barely avoids being killed or incapacitated.
• When a hero performs an impressive feat, such as chopping off an opponent’s limb or head (which I say happens by bringing an opponent to 0 hp with an attack that does at least 10 hp damage) or casting a clearly powerful spell.

You might skip a check if the creature believes itself to be winning.