Happy New Year! I think many of us are looking forward to the magical year of double-nat-20's and seeing what that will bring. I'm hoping for some interesting OD&D-type things on the blog here, as well as more livestreaming with Wandering DMs . In fact, we've got some things lined up this year that I'm pinching myself over because it seems almost too good to believe (while keeping our normal schedule of live chat Sundays at 1 PM ET). More on that later.One of the things I've been working on lately is assessing what early writers intuitions were about monster challenge levels. The earliest game (of course) didn't have any formalized notion of "challenge ratings" or the like. One early attempt was Don Turnbull's MonsterMark system. I have my own system for OD&D I call MonsterMetrics , which uses million-fold computer simulations to generate an estimated "Equivalent Hit Dice" (EHD) value; current valuations are available in the OED Monster Database on the website here Whenever I prep games nowadays, such as for classic modules, I make spreadsheet listing of all the contents and assess EHD ratings as a way to gauge reasonable PC numbers and levels going in. So I'll probably be sharing some of those in the near future.For starters, here's a refresher of what the 1974 OD&D Little Brown Books say on the matter: almost nothing at all. There aren't any guidelines for what a single expected party size should be, or how many monsters populate a normal dungeon room, or how powerful a given monster is vs. PCs, or anything like that. The entire arrangement is expected to be managed on an ad-hoc basis by referees on the fly, basically.Here's the closest we get to any hard advice, in the section on Wandering Monsters (Vol-3, p. 11):One of the things this highlights is that early on, there was the apparent expectation that DMs would modify the monster numbers and threat levels on the fly to balance against the party present. Some DM's intuitively do that today, but the general idea dropped out of the published rules and modules pretty quickly. For example, in the Holmes Basic D&D Zenopus dungeon you get advice to do that in the very first room, but not anywhere else. The same thing occurs in Frank Mentzer's version of the Village of Hommlet (but not in Gygax's earlier version).In this particular case, the wandering monsters seem to be balanced (at least on average) to about one-third the total strength level of the PCs. If you have 1-3 1st level PCs, on the 1st level of the dungeon, encountering a 1st-level monster, then apparently the advice is just to have a single such monster. For 4-6 PCs, you get two monsters, For 7-9 PCs, you get three, and so forth.I don't mind that, and I try to do roughly this in my games today. Nowadays (after the miraculous year where Gygax & Arneson had the only D&D games in the world and their basements were stuffed with 20 players 7 nights a week), it's become conventional to think of "standard" party size as something in the 4-6 player zone, so for like-level monsters, I roll a 1d3 for numbers (then multiplied by dungeon level and divided by monster EHD, if these differ from party level).But that's for wandering monsters. How many should you expect in a set-lair situation? The rules simply don't say. As a stab I might expect to double the number of a wandering group, so: roll 1d6 for a lair or something like that. If we look at rulebooks a few years later we'll see Gygax writing a lot of 1d4+1 or 1d6+1 numbers in those situations. That comes close to equating monster encounters with the total PC power level (like: 4 players running up against 4 monsters in the average case), for which we might expect just a 50% chance of victory in either case. (This gets modified by magic and strategy, as my EHD ratings don't take those into account at this time.)But all the OD&D books say is this (Vol-3, p. 7):That's totally it. In future posts hopefully we'll see some more specific things as that evolved in published books and adventures in the next few years.Open Questions: Do you massage monster encounter numbers to your player strength on the fly during games? In my case currently I would likely say "yes" in most one-off games (convention situations, etc.), and "no" in ongoing campaign situations (where the monsters have some background ecology and existence; so if PCs don't bring enough troops they shouldn't go in there). In the past I would probably have been more likely to say "no" uniformly, but that's me. What's your current practice?