There’s been a big discussion about how to use the “% In Lair” stat from Monsters & Treasure (table on pages 3-4) and in other books. A lot of it is a series of very detailed arguments, some points being based on references in other sources like Arneson’s First Fantasy Campaign, which in my opinion is not official rules, but Arneson’s “Here’s how I do it” book. There are no official rules on how to place and stock lairs, because it’s up to GM taste and the needs of the group.
So, I don’t think “% In Lair” is meant to be anymore complicated than “Are the PCs exploring the lair of the monster? Is the monster home right now, or out hunting?” But I have some ideas on how to handle random lair placement, which I thought I’d repeat here.
First: If you have a special lair to place on a map, place it first. It’s like placing special rooms in a dungeon vs. randomly stocking other rooms. You want to figure out where Castle Greyhawk and the Tomb of Horrors are before you decide where the den of a random wolfpack is. I don’t even count typical dungeons as “lairs”, even though they technically are the lairs of the monsters that live in them.
Second: How many lairs are in the area? Assuming you’re rolling up the contents of a hex or wilderness area, you’d want at least a few lairs, but no need to go crazy. I’d set the base number of lairs as d6/2, dropping fractions, to get a range of 0 to 3, with 1 or 2 being the most common result.
I’d actually roll two dice. In rural areas or anything else close to civilization, I’d pick the lowest roll. In true wilderness, I’d pick the highest.
Third: Where are the lairs? Any place that looks usable, actually. Since I consider lairs to be smallish, not necessarily worthy of a map, it’s more a matter of terrain and monster preferences. Basic lair types are:
|Dice Roll||Lair Type|
|0 to 1||Natural Shelter|
|2 to 3||Modified Shelter|
|4 to 5||Cave (1-4 “rooms”)|
Natural Shelter could just be a shallow hole inside a thicket, a spot between two boulders, or a hollow tree. The modified form is basically a multi-chamber burrow, a nest, or a campsite for bandits or other intelligent groups. Structures may be newly made, abandoned and repurposed by wild animals, or just the ruined remnants.
Either pick a suitable area on the map that matches the monster type or roll: d6/2 for plains, desert, swamp, or forest, d6 for hills/mountains (+/- 1 based on closeness to civilization, current or historic.)
Fourth: Is the encounter in the lair? If it’s a wandering monster, no, but you could roll a d6: on 5+, it has a lair nearby. Otherwise, it’s looking for a new lair. If the party finds the lair first, rather than the monster, that’s when I’d make the “% In Lair” roll to see if it’s home or out hunting. I’d roll again periodically as the PCs explore the lair, to see if it returns.
How do PCs find lairs? Usually by tracking creatures, or backtracking where a dead creature came from, if they encounter the monster first. If there are people living nearby, they might have clues as to where to look. There’s always magic, too. But if we’re not talking about wandering monsters, it’s mostly a matter of dumb luck: PCs see something they want to explore, perhaps to set up camp, and it turns out to be occupied. If it’s the lair of bandits or the like, PCs might see smoke from a campfire and head towards it. If the PCs are following a treasure map, the map destination may now be occupied.
Finally: What happens when PCs clear a lair? Monsters pick lairs because they need shelter or a place to store their stuff. If the monsters are killed, any other creatures looking for a lair may move in. I’d use the same 5+ on 1d6 chance to determine if a lair has a new occupant when PCs revisit it later. If the new occupant gathers treasure, it probably won’t have much of anything when it first claims the lair. A good guess: after one month, a monster will have acquired 10% of the usual treasure for its type, plus 10% per month. If you want a roll, use either a flat d10x10% or 2d6x10% roll (treating 6s as zero,) but cap the result based on the number of months.
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