Using OSR monsters in 5e, and simplifying 5e stat blocks

I typed out a pretty hot-aired response to someone on reddit, and it formalised a mental process I’ve been using which I’d like to get down on virtual paper. It’s all very loosey-goosey, but it helps clarify my thinking.


Original Question:

Anyone have experience or tips for simplifying 5e monsters into a more OSR style? What are your favorite tips and tricks?


My First Response:

Alas, for I have forked out for the 5e Monster Manual, but I think it’s probably easier just working from the older edition stat blocks – they’re a heck of a lot easier to improv too.

I focus on working out a rough HD for the monster, from which I can get most of the important numbers.

AC = 10 + HD, unless you have a simple armour system, in which case use that.

Attack bonus = +HD
Attack damage for humanoids = nearest die to HD + 4 rounded down. Use the next highest die if the NPC is skilled at fighting.
Attack damage for monsters = [1/2 HD]d[HD] damage, can be split

# of hits until death = HD. If a damage roll is more than 10, count it as 2 hits. Ignore hits of less than 5 damage.

Target number for strong stat = 10 + HD
Target number for average stat = 10 + 1/2 HD
Target number for weak stat = 10

So a monster I used yesterday for four lvl 3 5e characters was a summoned rubbery monster. My entire notes for it, scrawled down a few minutes before the session, were:

Rubber/tar-demon – HD8

– Bludgeon x2 – +8, 2d8

– Spew boiling tar – Dex save or 4d8 damage

– For every slashing or piercing strike against it in melee, attacker takes d6 damage from spraying tar

– burnt rubber smell, gaping mouth, stretchy limbs & stomach expanding like a balloon before spewing


Kept the PCs going for a few rounds, bringing even the ridiculous AC20 raging half-damage-suffering Barbarian down to 5HP.


Original Poster’s Response:

This is pretty great and I am stealing that monster; But I should have clarified that I meant how can I take an existing monsters stat block from the MM and boil it down into something like this. But it gives me some good insight on how to create my own monsters and I am sure it would be easy enough to adapt.
A few questions;
  • How do you determine which die size to use for HD? Is it just arbitrary?
  • I am terrible at math and don’t understand this formula haha [1/2 HD]d[HD] ; can you clarify?
  • I like the idea of number of hits before death, and that’s a good formula and a way to let the players still roll damage, which is fun. I think I will adapt that but have you ever just used straight hp? Easy enough to roll up.
  • Can you explain the target numbers for stats? Do you mean that if the monsters Strong Stat is it Strength, and it has an ability that requires a strength save from the player, the save is 10+HD?
  • Do you bother with monsters having their own bonuses to Saving throws or Stats? Seems like no, and I agree really. You could follow the same formula from Strong/Average/Weak stat easy enough and even on the fly.
  • Do you make your boss monsters the same way? Or make them more complicated?
Thanks for this! I am planning a werewolf encounter for tomorrow and I want to keep it fast and dramatic. It will write up my own stats based on this formula and the block from the MM.

My Incredibly Long-Winded Second Response:

Steal away!
  • How do you determine which die size to use for HD? Is it just arbitrary?
I generally assume d8 as it averages out the big and small, but most of the time I don’t actually used Hit Dice as dice at all. Especially so with 5e monsters, since they use so many more than the older editions.
  • I am terrible at math and don’t understand this formula haha [1/2 HD]d[HD] ; can you clarify?
I am certainly no mathematician either. I still have to stop and remember which way round > goes!
It simply means take the HD and halve it, and that’s how many dice worth of damage the monster can do in a turn. The size of the damage die is roughly equivalent to whatever their HD is (so an HD8 monster would use d8, an HD11 monster would use d10 or d12 – usually d12 because 5e PCs are tough.)
Actually, I missed out extra damage on the formula – add half the HD in damage onto the roll, essentially accounting for the attribute bonus.
Split the dice as you wish, if you think the monster would have multiattack.
Another example: an HD6 monster would do 3d6 + 3 damage. This could be one attack using three dice, three attacks using one die, or two attacks using two dice in one and one die in the other.
  • I like the idea of number of hits before death, and that’s a good formula and a way to let the players still roll damage, which is fun. I think I will adapt that but have you ever just used straight hp? Easy enough to roll up.
I have done, and it probably works well enough with one or two monsters, but it can quickly get tricky keeping track of it all. Not difficult, necessarily, but you’ll be scrawling down a lot of numbers which can make it harder to remember how well the monsters are each doing.
Using HD as number of hits, it meant that the session before I (as I say, not a mathematician and not great with numbers) felt pretty comfortable running a mass combat of four PCs and four of their NPC allies against some fifteen unique human foes each with a different spell. It just meant I used tallies rather than addition, which sped things up no end!
  • Can you explain the target numbers for stats? Do you mean that if the monsters Strong Stat is it Strength, and it has an ability that requires a strength save from the player, the save is 10+HD?
  • Do you bother with monsters having their own bonuses to Saving throws or Stats? Seems like no, and I agree really. You could follow the same formula from Strong/Average/Weak stat easy enough and even on the fly.
I don’t sweat too much about all the different saves and treat most of them as strong – reasoning that HD is good stand in for ‘how difficult is this monster?’. If the monster is forcing the PC to make a save, chances are it’s using a ‘strong’ stat. So yeah, it’s the Save DC, essentially.
I also find players don’t worry so much about what a monster is weak at compared to what the PC is strong at. If they force the monster to make a save, it’s d20 + HD. Mathematically it’s the same (like Perception and Passive Perception).
If there is something obvious though, like a Wisdom save for an ogre, then I essentially roll with no modifier.
  • Do you make your boss monsters the same way? Or make them more complicated?
Actually, that was the boss monster of sorts, albeit with a lot of those human enemies around. I probably would have put some more thought into it and its special abilities had it been alone, but the core numbers would have remained the same. Essentially, this HD system means I have a core base for monster onto which I can stick any special ability I like, which is what players actually remember from a fight.
  • But I should have clarified that I meant how can I take an existing monsters stat block from the MM and boil it down into something like this. But it gives me some good insight on how to create my own monsters and I am sure it would be easy enough to adapt.
This has already become rather long-winded, and I might have to come back to it, but I’m pretty sure you could condense most of the monster stat blocks to something like the above. As I say, it’s the special abilities which really make the monster, so take those and adjust things like DCs (and probably just summarise them – 5e is full of generally unnecessary legal-like clauses).
For a number to base the monsters around, I’d take the CR rating instead of HD, and just round up the fraction CRs to 1.
Let’s try it. I’ve just leaned across, grabbed my monster manual and opened to a random page.
Barbed Devil – CR5
Okay, so let’s work with that CR.
AC15
Attack bonus: +5
Damage: 2d6+3
Strong stat / DC: +5 / 15
Average stat / DC: +3 / 13
Weak stat / DC: +0 / 10
Not too far off the actual numbers. It doesn’t do as much damage in the monster manual, but it’s better against save effects.
Its special rules – Barbed Hide, Devils’ Sight and Magic Resistance – can stay as they are. In fact so can the attacks.
So if I were to try and condense the stat block, I’d probably go for:
Barbed Devil – CR5
 
Attacks, either:
– claws and tail – 2 x +6, 1d6+3 ; 1 x +6, 2d6+3
or
– hurling flame – 2 x +5, 3d6 fire
 
Resistant to cold & mundane physical; immune to poison & fire; advantage against spells & magic
 
Barbed hide causes 1d10 damage to grapplers
 
Sees through the dark and magic dark (120ft)
To be honest, if you’re looking to condense stat blocks down, just take the CR to guide you on stat DCs and the like, note down attacks and any abilities and resistances that differ from what you could work out in your head (for instance, do you need to write down that skeleton is immune to being poisoned and exhausted?). They won’t perfectly match what’s in the MM, but they’ll be usable at the table.
It must be doable. A chap on the OSR subreddit condensed a whole load of Pathfinder monsters, and brilliantly so. His two-sentence summaries are excellent.
Sorry, quite a lot of hot air.

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