But they're also often boring, and easy to ignore.
Pathfinder's random encounter tables are a vestige of the game's origins, back in original D&D's dungeon crawls and wilderness explorations. Random encounter tables back then put the screws to players, providing an ever-increasing tension and stress on resources. Random encounters - even the possibility of them - break up the idea of the five minute adventuring day because they guarantee the PCs cannot account for all threats in all directions. They also provide some world building, by showing you what kinds of monsters are native to or traveling through specific areas. And they're just great inspiration, putting the game into the dice and seeing what comes out. You often get surprising, unusual results. Fantastic ones that make your game more interesting.
In order for your random encounters to be richer, you need richer tools. So I've looked through a variety of sources and stole, adapted, or reconfigured tools for Pathfinder - for your game, no matter what it might be. It doesn't matter whether you're in the wilderness, underground, in a dungeon, or a city: what I'm about to lay out will make your encounters richer and more interesting. Better yet, these tools don't require you to change anything about your game. They just provide a setup for generating random encounters in Pathfinder. All you need is this page, some dice, and a random encounter table like the one shown above.
Ready? Let's get started.
Random encounters are really for the players as much as you. If the players know that random encounters will occur when they do specific things, when specific amounts of time and so on pass, it motivates them to keep careful track of their actions and their time spent. It makes the game more meaningful. Because of this, I strongly recommend you actually have your players roll for random encounters, not you. Don't tell them what the table results are outright, but do ask for d100 and d12 rolls and watch as they realize what they're bringing upon themselves. To go with that, lower results are generally more interesting on the following tables and results - this is the reverse of how tables usually work in Pathfinder, but it does add some spunk and spice to the usual cry of despair at rolling a 1.
First off, when do you roll for random encounters? Pathfinder is frustratingly vague about providing answers or guidance for this question. There is some information in D&D 3.5, but it's mushy and bad. We can do better by going back to the 1e DMG and similar sources. Before we begin, it's worth remembering that some sources do provide instructions on when to roll for encounters. As an example, Rise of the Runelords suggests rolling once per day or a night of rest. You might want to adjust how often you roll, decreasing it for safe areas or increasing it for particularly dangerous ones. As a general rule, however, roll according to the following.
Wilderness Roll every four hours. Generally PCs travel about 6 miles per four hours, so you'll have 3 rolls while traveling 12 hours, and 3 while asleep or resting. Nice and neat. Distance matters in addition to time when doing exploration gameplay (from Ultimate Campaign or Ultimate Wilderness). For exploration gameplay, roll every six miles travelled. (Note Ultimate Campaign's hexes are 12 miles across, so you'll want to roll twice per hex for those.)
Dungeon Roll every 30 minutes of activity, or every four hours while resting. Additionally, roll when the players make a lot of noise in game (a loud battle, a lot of firearms going off, explosions, whatever.) If you have players that insist on checking every nook and cranny, roll every time they take 20 on a Perception check to inspect something.
Why? Random encounter checks keep the game moving and stop it from getting stuck. By rolling in response to player actions (and time in Pathfinder is a function of player actions) you're reinforcing that player actions have consequences, and that those consequences can often draw out resources or attention.
The flip side of this is that if the game is running well and your players are ON, ignore the random encounters if you want. If they are doing stuff and people are having fun, don't slow them down. But if they're uncertain about their next move, if they're arguing, or if they're pointlessly searching everything, make it time for a random encounter. Make the game exciting.
The Encounter Roll
Every 4 hours? Every 30 minutes? My players are going to be drowning in monsters and we're never gonna get anywhere! Well hang on. I didn't say every roll was a full on monster encounter with a battle map and everything. That would be boring. We can do better than boring.
When you roll for encounters, grab 2 sets of dice. One is a d12, and one is whatever the table you use calls for. (So if I was rolling on the above Rise of the Runelords table, I'd have a d12 and 2d10 for a d%.)
Your dice for the table you're using are as normal. Those give you a monster, its source, and its number appearing (don't forget to figure that out while you're at it.)
Your d12, you check on this following table, which we'll call the encounter roll table:
1d12 Result (Chance of Occuring)
1-2 Monster (16.66)
1-2 Monster (16.66)
3 Lair (8.33)
4-5 Spoor (16.66)
6-7 Tracks (16.66)
8-10 Traces (25)
11-12 Nothing (16.66)
Monster The PCs encounter the monster you rolled with your other set of dice. Don't just go right to Initiative - I've got some more details for you below.
Lair The PCs find the lair of the monster. By lair I mean a reasonably sized space that the monster lives in, and presumably where it keeps its treasure and other interesting things. You can fit this in no matter where you roll this result, I bet - outside it's really easy to think of monster lairs, but in a dungeon fill up your next empty room. Yes, the dice have just completely changed the geography of your game. That's surprising to you and it's inspirational and isn't this hobby cool?
Again, lairs usually contain the monster's treasure as outlined in the monster stat block, except for anything the monster would actually carry on it.
When you're rolling to see if the PCs and the monster spot each other (see Encounter Distance below), if the PCs would spot the monster but the monster doesn't spot the PCs, the lair is actually empty. Yes, that means the PCs may get some treasure without fighting a monster. That's pretty cool!
Clearing out a monster's lair or slaying monsters in their lairs may result in permanently removing it from the encounter table. It's dead, or scared off, or just moved on. Obviously this most likely happens with unique monsters, or ones in small numbers. You're never going to kill all the goblins, they breed like rats!
Spoor A sign that the monster has just been here, like a victim's body, the monster's dung, or something else. The next time you roll on the Encounter Roll Table, take a -6 penalty. At your discretion, keep the same result from your encounter table so the PCs run into the monster they just found the spoor from.
Tracks The monster has passed this way recently. PCs can make Survival checks to track the monster. Some monsters (invisible, incorporeal, flying) might not leave tracks, but don't make all your monsters not leave tracks.
Traces A trace or other sign of the monster. Unlike Spoor, the monster hasn't been here recently, but this is a noticeable sign of its existence. PCs with applicable Knowledge skills can make checks at a -2 penalty to identify the monster when they find its Trace.
Nothing Nothing happens.
Now, this is the mechanics. For each of the results on the Encounter Roll Table above, you really want to come up with a unique narrative element for each individual monster on your encounter table. You design unique elements to give the monster a place in the world, some context and some influence before the PCs actually meet it. You could design all of them before play, in which case you can just add Lair/Spoor/Tracks/Traces as extra columns to your encounter table, or just come up with them as you roll them (in which case keep notes.)
You do want two Traces for each monster, both different, so that the PCs can get an idea of what the monster is like even if they don't actually make the Knowledge checks.
Here's an example from the Rise of the Runelords table, for the mite:
Lair A low, small cavern shared with vermin.
Spoor A gnome viciously stabbed hundreds of times.
Tracks Tiny three-toed tracks.
Trace 1 A scrap of cloth coloured a vibrant, unnatural green.
Trace 2 A dead dog-sized spider with riding saddle attached.
See, aren't those cool? And all that from the mite's entry in the Bestiary and a little thinking.
If you're going to have an encounter, you're going to need to have an idea of the terrain. It's all too easy to just set up the same battle mat and put people roughly 60 feet apart and everything feels the same all the time. We can do better than that. Figure out the rough terrain of your encounter, and then roll on the following table. Keep your result in mind, you'll need it again:
Spotting Distance By Terrain (Or Other Factors) Distance In Feet
Smoke, heavy fog, other dense concealment 1d4 x 10 feet
Murky water 1d8 x 10 feet
Jungle or dense forest; rugged hills 2d6 x 10 feet
Medium forest; swamp; urban 2d8 x 10 feet
Gentle hills 2d10 x 10 feet
Light forest 3d6 x 10 feet
Scrub, brush, or bush; marsh or moor, sandy deserts 6d6 x 10 feet
Clear water 4d8 x 10 feet
Mountain, valley, or canyon 4d10 x 10 feet
Flat desert 12d6 x 10 feet
Plains or grassland 12d12 x 10 feet
Total darkness or indoors (dark) Limit of shadowy light from light sources or other senses (darkvision, blindsight, tremorsense, etc)
Indoors (lit) Line of sight
Underground As most similar aboveground terrain to limit of light if necessary (other lights can be seen at standard spotting distance)
So now you know roughly what distance your PCs and your monsters might perceive each other at. Spotting is really only half the story - the parties could hear or smell each other, for example. It's just a rule of thumb. Don't worry about direction, or actually being able to see each other - this is just their general distance when they might become aware of each other.
To check if the groups become aware of each other, have them make Perception checks (the DC is the number you rolled to determine their distance apart.) If either side is trying to be stealthy, skip to Stealth below instead of rolling this.
Some common modifiers that might apply to this roll for one or both sides:
Size -1 for each size category the other group is smaller than Medium; +1 for each size category the other group is larger than Medium
Six or more creatures in the other group +5
Bright Light (noontime) +2
Dim light (dusk, tree cover) -2 (low-light or darkvision negates this penalty)
Starlight (darkness) -4 (darkvision negates this penalty)
If at least one character or creature succeeds at this Perception check, the encounter begins at full distance. Place the characters on the map and roll for initiative; successful characters act in a surprise round.
If no one succeeds at this Perception check, the encounter begins at half distance. Place the characters on the map and roll for initiative; there is no surprise round. Both sides essentially run into each other.
Note that full or half distance, either group might not be able to see each other - successful Perception checks could be hearing the other group, not seeing them. Find out what happens when your PCs hear orcs coming for them from one room over, but can't see them yet.
If either or both side is trying to be stealthy, encounters always occur at half rolled distance. Stealthy creatures always receive surprise. Other creatures roll Perception, with a DC equal to 10 + the Stealth modifier of any stealthy creatures. Characters that succeed on this Perception check are not surprised and may act during the surprise round.
One thing Pathfinder always assumes is that any given monster or encounter is always going to be hostile. It doesn't really state it specifically anywhere, but the default assumption is that an encounter is going to be combat. Not everything turns out that way though. Goblins are sometimes enemies, sometimes friends. Some creatures from the Bestiary are actually helpful to adventurers. And not everything wants to fight - a pack of wolves could just warily look on and then fade into the distance. Pathfinder even has room for more than just outright hostility - Diplomacy allows you to change a creature's demeanour, and so does charm person.
Old-school D&D had a term for this called the reaction roll, and I've duplicated that here. It's your last step in rolling because it determines what your monster will do when it actually hits the table. It doesn't necessarily need to fight! But you need to apply a bit of thought as to whether it's appropriate to make a reaction roll or not - monsters are still monsters after all, and in a big evil lair they're probably going to regard intruders as intruders no matter what. Fighting is often the first resort for many creatures, and for good reason. Conversely, mindless (Int --) creatures probably only react in instinct or according to simple instructions, and don't have different responses that the reaction roll would apply to. Unintelligent (Int 1-2) creatures may or may not have different responses, but are probably governed by their base needs. Again, use your own initiative and see what makes sense. Don't let the dice overrule you on this roll.
Reaction Roll Creature's Demeanor
1-2 Hostile, attacks
3-6 Unfriendly, may attack
7-10 Indifferent, uninterested
11-12 Friendly, may offer aid.
These categories are the same ones used in Diplomacy, Intimidate, and so on, so that your group can bring skill checks/magic/roleplaying to bear as they see appropriate.
One big change that I would recommend from the Pathfinder standard is not to have treasure carried by random monsters (except any gear they are equipped with or things they would be carrying.) Random monsters are cool, but you don't want them to be reliably rewarding (except for XP, don't shaft your players on that.) By keeping treasure as a function of interacting with the actual campaign, you're motivating your players to dig into your dungeons, complete your quests and so on. Not all Pathfinder monsters carry treasure by default anyway, so this shouldn't be too big a change. You can use random monsters as your treasure-free monsters to balance out NPC gear distribution (see Core Rulebook page 400), place treasure elsewhere to make up for the experience gained from random monsters, or just not worry about it. Most PCs end up way ahead of the expected wealth per level anyway.
That's my suggested additions to generating random encounters in Pathfinder. I hope you find these helpful, and that they help you as a GM flesh your game out a bit. Please provide any questions, comments, or suggestions below.
There wasn't an absolute ton of original design that went into this article. It was more synthesis and conversion from other systems and ideas. Credit goes to the following:
1e Dungeon Master's Guide
3.0 Dungeon Master's Guide
Pathfinder Core Rulebook