Telecanter’s Receding Rules has an excellent post on wandering monster checks, covering the different ways in which various old-school rulesets handle wandering monsters: how often the DM checks for them, encounter distance, increased probabilities if the PCs are making noise or loitering at a major intersection, etc. Telecanter also offers his own house rules for handling wandering monsters.
The details of wandering monster encounters are important for the old-school DM to consider. I’ve been using the Holmes rules (roll once every three turns), with additional rolls when the PCs do stuff to attract attention. Now I’m considering moving up to the probabilities in Moldvay (roll every two turns). Rolling every turn, as in OD&D, seems too often to me, unless it’s to make up for absent-mindedly forgetting to roll half the time.
What method do you use for wandering monster checks in your game?
The Mule Abides 
I’ve always used 1 in 6 for the probability, but I’m only slightly sure I followed the every 3 turns rule. These days, I’d roll 2d6, and if it comes up doubles, there’s a wandering monster at the distance indicated on one of the dice… but I think I’d lower the frequency of rolls to once an hour while not moving, plus an extra roll while moving, plus extra rolls any time the party does something that could attract attention.
I do not typically stick to any one way to determine wandering monsters. There are just too many variable to consider, though once considered, I might go with one over another.
Things I might consider before deciding on what dice/; type of monster, number of monsters, size of the dungeon, the feel that I am going for (ie scary, might mean less random but tons of hints in the form of ‘encounter’), etc.
To elaborate on that last thought, I do not consider a “Wandering Monster” an actual monster every time I roll for it. It might just be signs of a monster; dung, fresh kill, jagged claw marks on the walls, sounds, etc.
Thanks for getting me thinking on this. Perhaps I need to standardize and jot down my thoughts on this…
TB
I rolled only on entering a complex when I played Moldvay/Cook (ie, only when the module reminded me about Wandering Monsters) … but in AD&D I was pretty consistent with one roll per turn. It was all behind the screen so if the PCs couldn’t handle it, I just skipped it.
Call it, WM for inspiration only.
Of related interest, there were a bunch of hidden facts about the wilderness encounter table that added up to weird activity while traveling through wilderness hexes.
Dragons and other nasty beasties were relatively common on the outdoors table. The encounter distance roll combined with the reaction table roll combined with the rules for evasion meant that the best way for a party to survive in the wilds was to wait to see if the dragon wheels over to come back and then run like hell in pairs in different directions and hope you were not the twosome that was chosen to be eaten. Yay survival!
Telecanter: “I remembered wandering monsters when 1) players were doing something kooky or noisy, like busting down doors, or 2) there was a long lull in action because the players were being indecisive.”
In my experience this is the approach that works, and cuts closest to the reason for having monster checks in the first place. Keeping strict track of time in the dungeon in theory sounds great but in practice gets in the way of game spontaneity.
Has anyone had a WM encounter very close to a scheduled encounter and have the two groups interacted? Did they fight each other or stick with the ‘… vs. the World’ mentality of the game and both attack the party?
Yes, in module B2: The Keep on the Borderlands. A PC’s shouted challenge drew the attention of some bugbears that followed the party to the wizards (changed from the module’s evil priests) at the far end of the ravine. The bugbears attacked the handful of PCs who stayed outside of the wizards’ cave while those inside were fighting a defensive force of zombies. When a couple of wizards showed up on the scene, the PCs persuaded them to put the bugbears to sleep.
I really like encounters with multiple sets of enemies, whether Wandering Monsters or not. There is something extra frenetic about them, not just in angle but in type. Bountiful for the senses, so to speak. In the last adventure I had a room full of blindly hopping Cave Locusts on one end and a marching cadre of gnomish zombie-mummies trooping up the corridor. Didn’t quite work out the way I was hoping, but the mash of styles was promising. I liked how the locusts do damage only by accident and land at random, so they could have taken out some of the gnome-things as well.
I’m wandering away from wandering monsters. But like an amazing song mash-up, wandering monsters clashing with set encounters can be glorious.
In a run of Blackmoor Dungeons at Gen Con, the players loaded themselves with three tons of gold (leaving 20 tons of silver behind!) and set out to follow their map back to safety with almost an hour remaining in the session. This was one of the few times I’ve had the time, attention, and dramatic impetus to really count out how many squares they were moving each turn and roll the wandering monster die. It was great fun and really added an element of tension; when they made it back to the surface without an encounter, having been rigorous about these rolls created a sense of successfully having overcome my best attempts to keep them from leaving.
In this case, I unconsciously reverted to the every-two-turns, 1-in-6 from Moldvay.
Also BTW, Javi and I played in Telecanter’s game at the So Cal Mini Con II and it was hella fun.