Below is the table I'll be using for the Perilous Halls of Sorrow Random Encounters. It only goes to level 10, but I only rank my dungeon level in danger from 1 to 10. There is a 1 in 6 chance for a random encounter once every 30 minutes. All other encounters are based on exploration and character actions. Certain things, such as making god awful amounts of noise, will also spur a random encounter check, but the results will be modified to fit the circumstances.
|Vermin||01 - 50||01 - 40||01 - 32||01 - 26||01 - 21||01 - 17||01 - 14||01 - 11||01 - 09||01 - 07|
|Lair||51 - 65||41 - 56||33 - 49||27 - 44||22 - 40||18 - 37||15 - 35||12 - 33||10 - 32||08 - 31|
|NPC||66 - 70||57 - 62||50 - 57||45 - 54||41 - 52||38 - 52||36 - 54||34 - 56||33 - 59||32 - 63|
|Events||71 - 80||63 - 72||58 - 67||55 - 64||53 - 62||53 - 62||55 - 64||57 - 66||60 - 69||64 - 73|
|Creatures||81 - 00||73 - 00||68 - 00||65 - 00||63 - 00||63 - 00||65 - 00||67 - 00||70 - 00||74 - 00|
Nasty weird vermin that inhabit the dungeon. Strange types of spiders, huge grubs that cause infected wounds, giant bugs, freaky rats, tentacles, worms, grabbing claws, and all other manner of nasty or irritating stuff. Low level characters might take a beating, but more advanced adventurers will face some harassment, little more. If nothing else, it adds color to the crawl.
This will be an encounter from a monster or monsters from the nearest area designated as a lair. The Lair may be on the same level, or an adjacent sub level. For example, goblins from the Bloody Feet tribe have a lair somewhere near the Signs of Madness level of the Halls of Pain region - so they are going to pop up from time to time.
An encounter with one of the NPCs from the dungeon. The tables from the Dungeon Dozen are a great example of what can be done. This is also where the classic "NPC Party" fits in. If an NPC is no longer available, then there is no random encounter, just a feeling of hollow loss.
Dungeon level events are classified as either repeating or one-time events. These are designed to add tone and flavor to the level, introduce side-quests and sub-levels, but can also include some hazards and challenges. The Wandering Pit is always something to be feared. Ghosts and spirits of previous dead adventurers may give information for eternal peace or acts of revenge are said to be common as well.
These are monsters that wander the level looking for something to kill, murder, maim, eat, destroy, or otherwise toy with. Each type of creature has a number appearing but also a maximum on the level - if all of a particular creature are destroyed, then they are no longer available (at least, of course, until the dungeon restocks itself).
Simple Level Variation
Roll 1d6. On a 6, roll another d6, repeating as needed. For each 6 rolled the encounter is from 1 level lower than the current dungeon level the characters are exploring. The same thing applies if a 1 is rolled, but the creatures are from higher dungeon levels. This doesn't apply to Vermin and only rarely applies to Events. While this could apply to Lair encounters, instead make the encounter from the lair more or less powerful.