Mr. Cook writes:
Encounters are usually checked for once per day, but the DM may include planned encounters, or may make additional checks if appropriate. No more than three or four encounter checks should be made per day.
Again, the time scale, like those for distance, is grossly large.The assumption is that the PCs will travel through a hex, jot down the principal terrain type, and then move on. Making only one or two wondering monster checks per day means that you can quickly mark off a handful of days fairly quickly. Cook suggests rolling a d6 to see if an encounter happens; in grasslands and hexes occupied by a civilized settlement, encounters have a 1-in-6 chance of happening. Most terrain has a 2-in-6 chance of generating an encounter, while jungles, swamps, and mountains have a 50% chance of generating an encounter.
That’s not a lot of encounters. Traveling across your fantasy version of the American Great Plains will allow your average group of PCs to cover 18 miles in a day (three hexes) and encounter wandering monsters only once per six days on average (or basically once every 108 miles).
In short, logistical shortfalls are of greater concern than monsters. That D&D is about exploration more than monster-mugging becomes abundantly clear in a hex-crawl. Logistics are a bigger issue than combat (and so we’ll take a closer look at it later, when we discuss hex-crawling from the picture side of the DM’s screen).
But wait, there’s more! If you use Moldvay’s Monster Reactions table (page B24 for those of you following along at home), combat becomes even less likely. That’s because it’s a 2d6 roll with the most common results (a roll of 6, 7, or 8) being “Uncertain, monster confused”. You’re just as likely to roll “Enthusiastic friendship” (a 12) as you are “Immediate Attack” (a 2). (Cook reproduces the table on page 23 of the Expert book when discussing outdoor encounters.)
And, just to lower the chances of combat even further, there is a chance for the PCs to evade the monsters. The table given decreases the chances for larger parties of PCs, and increases the chances for larger groups of monsters. A party of 5 to 12 PCs, hirelings, etc, has a 50% chance of evading a group of monsters numbering between 4 and 8, and a 70% chance of evading groups larger than that. Failure to evade still allows the PCs to flee “in a random direction (no mapping)” with a 50% of being caught if the monsters are faster. “This procedure is repeated until the party successfully evades or is caught. (This may result in the party being chased for several days, if the pursuers are really serious about catching them.)”
Two other things of note on wandering monsters: first, many are bestial, and so won’t be carrying treasure on them, unless the PCs are lucky enough to encounter them in their lair. Second, there is absolutely nothing done to match the levels of the PCs with the toughness of the monsters on the charts. In most terrains, Cook’s tables return a dragon (which could be a chimera, wyvern, basilisk, or salamander in addition to one of the classic color-coded wyrms) in one of eight encounters on average (one in four if the encounter is mountainous, hilly, or barren terrain).
The moral of our story here is that combat isn’t the fun in a hex-crawl. The real fun is exploration and discovery, and even a mid-level party is going to want to avoid most combats and needs to be willing to sacrifice their mounts if they encounter a hungry dragon or the like.
With this in mind, our two goals in creating a wandering monster table need to be 1: a random complication to the otherwise straightforward logistical challenges over overland travel and 2: an opportunity for interesting RPing encounters. We’ll tackle actually building some tables next time.