I’ve seen some questions lately about to what extent 5e is compatible with OSE monsters and especially vice versa.
I wonder if such questions kind of stem from a remnant of the 3e/4e philosophy of serving up a sequence of balanced encounters.
A monster has four components:
And specials. Which can be completely out there. “This monster can walk through walls”, “this monster makes the law a real physical force that you are physically unable to break”, “this monster can walk on ceilings as if they were the floor”.
Monsters have these five components in both 5e and OSE.
Yes, there is a little bit of a trend in 5e (and in SWN/WWN) that HP and damage is a little higher for a given challenge rating, while AC and accuracy is a little tighter.
Fighting against OSE monsters is a little more “clang, clang, clang” while fighting against 5e monsters is a little more “chop, chop, chop”.
The tribe of white crabs in Deep Carbon Observatory (HP 3, AC 3 [16]) is a perfect example of this difference.
Someone with attack bonus 4 and 1d8 damage would need around 2.7 rounds to defeat such a crab. Similar to a monster with more HP but lower armor, like let’s say HP 5, AC 6 [13], that’d be around the same amount of rounds. Those rounds have a slightly different feel, with the better AC crab having a few more rounds of whiff, but both basically can work in the same game. It’s not a game breaker either way.
As an aside, this was deliberate when making 5e; they wanted the range of armor and accuracy to be a little bit tighter over the 20 levels. I think it’s a good thing for sandbox play; 100 peasants can take down a giant in 5e. Or they could take down a cocky high-level PC. In OSE the fighter goes from +0 to +9 over the 14 levels that game covers, in 5e she goes from +5 to +10 over that same fourteen level spread. That’s half the rate of increase, five steps as opposed to nine steps. And armor class rangers are similarly constrained, while hit points and damage output is a little bit higher.
As I tried to show with that crab fight, though, monsters can still work. They have a little more armor and a little less HP which translates to about the same number of rounds on defense.
The same OSE monster has one difference when encountered in 5e vs in OSE, though. Their attack accuracy.
Looking at OSE’s combat tables, it’s pretty much +1 to hit per HD. In 5e’s rules for using B/X monsters it’s 2+half HD (and there’s a cap at +12). So it starts higher but doesn’t increase as quickly, again for a narrower range, which I like for sandbox exploration.
HD 2 monsters hit a little harder in 5e, HD 3 and HD 4 monsters hit the same, and HD 5 (and above) monsters hit a little harder in OSE.
OSE doesn’t have a challenge rating because it doesn’t have the 3e/4e mentality of serving up a sequence of “balanced encounters”. Instead there is a dangerous world that the players can take on. The entire world is the encounter.
OSE says:
Normally, 1 HD monsters live in the 1st level of a dungeon, 2 HD monsters in the 2nd level, and so on.
That’s the way to think of these things. A larger party might proceed a little quicker through the dungeon, or a 5e party might have some pros and some cons compared to an OSE party, but it basically works. Back in the B/X day when groups were like 10 people (some of them henches and hirelings) things were a little bit different and that’s fine.
That’s how I think of it in 5e too. I don’t necessarily stick to the HD per dungeon level thing, but the general idea of comparing monsters to each other, not the PCs, and placing them accordingly. At first I was using fine-grained gradation between areas in my homebrew, based on XP budgets and such but nowadays I just look at the tier. T1 stuff nearby, T2 stuff a little bit further away, T3 stuff pretty well hidden, and that’s it.
Listen, let’s take a monster from the 5e module Cry of the Sea as an example. A HP 58, AC 3 [16], THAC0 14 (+5), #AT 2 2d6+3/2d6+3 damage monster with some nasty adhesive tentacle specials.
The levels, and amount, of PCs that the monster is appropriate for in 5e is different than the level and amount of PCs that the monster is appropriate for in OSE. It’s about as dangerous as the Cyclops is in OSE.
That doesn’t matter, because it’s not your job as referee to serve up monsters appropriate to the PCs. Your job is to place them in the world and then the PCs will go there when they are ready. 58 HP? 58 / 4.5 = 13, so place it on dungeon level 13, or 13 hexes away from the starting village, or w/e. You’ll be fine.
5e deliberately has a tighter, narrower range of levels so the characters can explore a bit more freely, go further, explore deeper. They still die though.
I’ve not had the fondest words for Microlite 5e, Five Torches Deep, and Into the Unknown in the past. I think they do surface level changes that doesn’t really make the game any simpler or more challenging. My favorite O5R game was Dungeonesque Red Book until 5e came out with its own O5R box, the Essentials Kit. Remove the skills, nerf food- and light-spells, track encumbrance, and you’re good to go.