Playtest Update #1: I am revising how to do quick and dirty hit points based on my playtest experiences tonight.
As I was mulling over my recent Swords & Wizardry Complete acquisitions it occurred to me that at its core there is a single on-the-fly method to use S&W stat blocks with minimal or...seriously...almost no "real" conversion at all in D&D 5E. In fact most of the conversion work would be in guesstimating DCs for saves and skill/ability checks; the stat blocks themselves can be used with some simple rules in place for quick on-the-fly numeric conversion. The new method below will work with any 1st edition stat block as well, and I think is a bit cleaner than my prior system for conversion.
Here are my conversion method suggestions so far:
Preamble: before converting something in a S&W Complete tome from Frog God make sure they didn't do it already in Fifth Edition Foes; and remember a significant number of the creatures in Monstrosities are already in the 5E MM.
1. Hit Dice
I've mentioned in a prior conversion that you could figure "5E HPs" by looking at the hit dice of the monster and comparing that to the equivalent CR on the table on page 274 in the 5E DMG; there's a simpler formula that gets a good approximation:
The Dirt Simple Hit Point Method: Roll HD as normal (or figure from an average; usually 4.5) and multiply by 4. This will generate a wider range on the hit dice and avoid uniformity. You should still roll regular hit dice for humanoids (like humans and elves) that normally progress with levels, however. PLAYTEST UPDATE: I didn't like the hit points this way in tonight's game, and have revised this to work as follows: use regular hit dice rolls for level/class based humanoids. Take the hit dice, roll or multiply by the average (4.5) and then multiply by 2 otherwise (shortcut: take HD and multiply by 9). X4 is a lot of hit points...do not use unless you want to challenge the party, or have a lot of high damage dealers in the group.
2. Armor Class:
S&W's armor classes include an ascending scale that is very close to what 5E uses....you rarely see S&W ascending ACs that are higher than what you normally see in 5E. If you're using a non-S&W stat block for conversion, or a module for S&W that uses descending AC, remember the formula: subtract descending AC from 20 for 5E AC.
On the saves, I think you could give S&W conversions a bit of oomph and also simplify your math by dividing HD by 3 and rounding down; apply this modifier to any saves the creature makes in lieu of determing attributes. If the creature has a noteworthy stat mentioned in its description, apply a +3 or +4 bonus for that stat's saves only.
4. Attack Rolls:
There are a few ways to do this, neither is any better than the other, but I settled on the following because it is easiest to do on the fly:
The Dirt Simple Attack Bonus Generator: use the HD as the attack bonus. This may mean the monster is 1-2 points higher on average (or lower) than the option one conversion, but it works just fine and is going to give you a range that will be level appropriate or even superior to other monsters without being out of bounds. Bump this up by +2 if the creature is noted for exceptional strength (or dexterity if ranged or finesse) on specific applicable attacks.
5. Initiative Bonus:
In 5E very few monsters have an initiative modifier beyond Dex. My suggestion is divide HD by 3 (round down) and provide as the init mod/Dex mod. If the creature has a noteworthy Dex, use the mod you settle on instead.
I have worked out three methods, but personally default to the preferred version:
The Preferred Quick and Dirty On the Fly Damage Conversion: add the hit die number to each damage set rolled. So a 5 HD beast with 3 attacks dealing 1D4/1D6/1D6 (average damage 9.5) now deals 1D4+5/1D6+5/1D6+5 (average damage 24.5). If you want a really tough boss monster then add double the HD to each damage roll.
If you compare the above to our HD determination method, to use the example a 5 HD monster has 90 hit points (average) on conversion....going by the DMG chart on page 274 that means it's average damage expression is around 15-20, so we're higher than the average for defense CR right now, which is just fine, I assure you.
Option 1-The Extra Dice Method: treat hit dice as extra damage dice instead. Add those damage dice evenly as multples to the existing attacks. So in the case above with three attacks dealing 1D4/1D6/1D6 from a 5 HD monster, you have 5 extra damage dice to deal: adding it evenly works out as follows: 2D4/3D6/3D6 (for average damage of 24); you can fudge it to make attack expressions line up properly (in this case we assume the D6 attacks are claws so they'd be equal).
Option 2-The Extra Deadly Straight Multiplier Method: if you want the monster to be a terrifying threat, do this. Just multiply the damage rolled by the hit dice of the monster. It's up to you if you multiply any adds, but strictly by the 5E rules you shouldn't. So a 5HD monster with 1D4/1D6/1D6 expression in this gets a damage average of 47.5....yowza!!!! but it does make the monster hit much tougher.
7. Save DCs
Just use this formula for a good average: 8+HD=Save DC. Maybe give it +2 if it has exceptional ability of note in the stat that fits any spell casting ability. If the creature has more than 10 HD then increase the Save DC by 1 for ever 5 additional HD after that (i.e. HD 11-15 = DC 19; HD 16-20 = DC 20, etc.)
8. Converting Save or Die Effects:
For save or die effects, to convert to 5E I suggest the following: figure the damage type (i.e. necrotic or poison), then change it to a save vs. DC against appropriate stat from step 7 above. Then have the attack deal dice of damage of that type equal to the HD or the monster, using D8 (or higher if it seems appropriate). Problem solved. EX: A 7 hit die creature has save vs. poison or die. Convert this into a Save vs. Con DC 15 or take 7D8 poison damage (or 1/2 on successful save). Convert other effects precisely, but maybe add a save after 1/0th of the time has passed for the effect to shake it off. EX: save vs. paralysis or become paralyzed for 1 hour. Allow a save to recover after 6 minutes. Another example: creature does a paralysis for 1 minute, so let the victim save after 1 round.
A little secret: this is going to be a houserule for my upcoming S&W Complete game; I never liked save-or-die even in the 80's, so all save or die effects in my games will deal damage equal to the hit dice instead.
9. Magic Resistance:
You can use the percentage as-is, or just subsitute the 5E standard magic resistance. I do the latter (easier) but either method is fine. Feel free to beef up resistances and immunities on the creature if it looks like it could use some.
10. Converting "hit only by magic weapons:"
In 5E this is always resistance against normal damage, but silvered/magic weapons bypass.
11. Level Drain
Convert that into 5E's "reduced hit point maximum" rule with Save DCs vs. constitution.
Divide by 4 and multiply that result by 10 feet for movement.
13. Everything Else:
When you're done, you might see something that makes less sense in 5E without it. For example, MR is a big deal in S&W Complete, but not as much in 5E....a lot of creatures that used to be highly magic resistant now express that through additional resistance/immunity in 5E, so feel free to beef defenses up if needed.
12. Pulling it All Together: The Cheat Sheet
Here's my "preferred list" cheat sheet for conversion. Print it out and stick it inside Monstrosities and Tome of Horrors Complete....congratulation, you've just doubled (or tripled) your monster options for 5E.
THE QUICK AND DIRTY S&W to 5E CONVERSION CHEAT SHEET:
- Size: medium, unless text suggests a larger or smaller creature.
- Hit Dice: Take HD number and multiply by 9. Roll HD as normal (figure a Con mod) for level/class based humanoids.
- Armor Class: use the ascending AC as is.
- Initiative: divide HD by 3 and round down for init mod/Dex mod.
- Save Modifier: use HD as CR to look up save bonus; for quick conversion divide by 3 and round down.
- Attack Bonus: use the hit die as attack bonus (so 5 HD = +5 attack).
- Damage: add HD as a bonus to damage to each damage roll; for boss monsters double the bonus.
- Save DC: 8+HD=save DC. Add +2 if it's a spell casting monster or boss monster.
- Movement: divide by 4 (round up) and then multiply by 10 feet
- Convert Abilities/Save or Die Effects: use the force to guide you; for save or die deal damage of appropriate type equal to HD in damage of monster (with save for half). Convert MR to 5E, and magic weapon immunity to 5E resistance.
- Challenge Rating: calculate it using the 5E DMG or just make it equal to HD
Now, calculating the CR....this is obviously easy enough to do with the final conversion averages, using the rules on page 274-277 of the DMG, and good to try out since it will give you an idea of what converted S&W monsters look like in 5E under this method. If you are rushed (doing a conversion on the fly) but use the cheat sheet version above, just look up CR by hit die and call it a day.
Malcarna (from Monstrosities, page 313)
Chaotic Evil large fiend
CR 6 (2,300 XP)
Hit Points: 45
Init Mod: +4
Armor Class: 16 (natural plus shield)
Magic Resistance: rolls advantage on saves vs. magic
Resistance: fire, only magic or silvered weapons do regular damage
Immunity: charming, banishment
Saves: +2 on all saves; +6 Charisma
Multiattack: 1 tail plus 3 weapon attacks
Tail Attack +5 to hit (reach 10 feet, 1 target) 1D8+5 bludgeoning damage
3 long swords +5 to hit (reach 5 feet, 1 target each) 1D8+5 slashing damage each
Movement: 30 feet
Hideous Beauty: targets must make a Wisdom save DC 13 to even attempt to hit a malcarna. Creatures of level 4 (or HD 4) or less roll at disadvantage to this save.
A hideous four-armed snake-tailed demon reminiscent of the Marilith, a half-demon often born of Marilith and mortal relations.
Spire Monkey (from Monstrosities, page 456)
Unaligned small beast
CR 1/2 (100 XP)
Hit Points: 18
Init Mod: +0
Armor Class: 12
Saves: +0 on all saves; +4 Dexterity
Multiattack: 3 claw attacks
claws +2 to hit (reach 5 feet, 1 target each) 1D3+2 slashing damage each
Movement: 40 feet (both normal and climbing speed)
Spire Monkeys are two-headed, six-armed little simians that live on rooftops and trees.
Xole (Monstrosities, page 520)
Chaotic Evil medium elemental
CR 6 (2,300 XP)
Hit Points: 91
Init Mod: +2
Armor Class: 17
Immunity: fire, cold
Saves: +2 to all
Multiattack: 2 (weapon and tail)
Stone Mace +7 to hit (5 foot reach, 1 target) 1D10+12 bludgeoning damage
Tail Swipe +7 to hit 10 foot reach, 1 target) 2D6+7 bludgeoning damage
Movement: 30 foot (earth-phasing or regular)
Earth-Phasing: xole move through earth in a semi-incorporeal state. It takes 1 movement action to begin the process, then they move normally.
Evil Elementals: Xole are evil and can be affected by protection from evil.
Elemental Mace: the mace can only be lifted/wielded by elementals of stone and earth.
Xole are similar to salamanders, but native to the plane of elemental earth; 7 foot long humanoid torsoes and 10 foot long tails.
Cinder Ghoul (Tome of Horrors Complete S&W version, Page 270)
Chaotic Evil medium undead
CR 5 (1,800 XP)
Hit Points: 54
Init Mod: +2
Armor Class: 15
Immunity: necrotic, fire, psychic, poison, disease, does not breathe
Saves: +2 to all
Slam +6 to hit foot reach, 1 target) 1D8+6 necrotic damage plus 1D6+6 fire damage plus target must make a Save DC 14 vs. Constitution or it's hit point maximum is reduced by the necrotic damage dealt and can't be regained until after a successful save at the end of a long rest. If the target is reduced to 0 HP on its maximum it dies (and probably comes back as a cinder ghoul).
Movement: 30 feet flying
This ghost-like monster of ashes and charred body parts is a terror to behold.
(Conversion Note: the ToH stat block doesn't mention fire immunity but...come on, it's gotta have it; the rest are implied for 5E undead immunities)