Using B/X Classes in Shadowdark RPG

What are the major considerations if the game is Shadowdark but the PCs are B/X?

Converting Experience Thresholds

We'll definitely want to use Shadowdark's experience system, it's too good and too easy for the DM. We'll use the Fighter as our baseline for raisons; the fighter will level up using the standard Shadowdark thresholds. By finding the divisor between Shadowdark xp thresholds and those for the B/X fighter we have what we need to create new xp thresholds for any class, practically on the fly.

-Level-	Divisor-	Cleric-	Fighter-	Lazer Mage-	Swarm Lord-	Thief-
1	0	0	0	0	0	0
2	200	8	10	13	20	6
3	133	23	30	38	60	18
4	133	45	60	75	120	36
5	160	75	100	125	200	60
6	213	117	150	188	300	94
7	305	164	210	262	393	131
8	414	242	290	362	604	193
9	649	308	370	462	616	247
10	783	383	460	575	766	358

This leads to some funky numbers that I'm fine with.

save vs unified mechanics

Shadowdark's use of stat checks is somewhat intertwined with the levelling scheme of the classes, namely the random rewards frequently increasing stats most associated with the class. Some napkin math reveals that the average Human Fighter will only gain +2 in their choice of physical stats three times from levels one to ten, the dispairity shouldn't be that woeful for B/X classes.

So option one is keeping the Shadowdark unified mechanics for saves. We could decide that each saving throw category should fall under the stats for which the B/X classes that have the best throw are associated with. That might look something like this:

-STR-	Breath Attacks (B)
-INT-	N/A
-WIS-	Wands (W)
-DEX-	Paralysis or Petrification (P)
-CON-	Death or Poison (D)
-CHA-	Spells, Rods, or Staves (S)

But based on absolutely no methodology, here is the quick pan-D&D save conversion scribbled on the inside of my own Shadowdark DM screen:

-STR-	Paralysis/Petrification
-INT-	Spell/Rod/Staff
-WIS-	Hold/Madness/Will
-DEX-	Wands/Breath/Reflex
-CON-	Poison/Death/Fortitude
-CHA-	Fear/Charm/Polymorph

To emulate the way B/X PCs get better chances at making saving throws over time, make saves Hard at first and then use the lower DCs as they level. I guess.

Option two: just keep the B/X saving throws. You're using B/X characters, it's already on the sheet. This is the better option.

Skill Issue

How skill rolls work in Shadowdark is ace, let's not change that. When a class would give you a better chance than normal to succeed at something, such as the Dwarf listening at doors, you are instead considered proficient in that activity as if from your background or downtime studies. If a class would give you at least a 65% chance to succeed (such as a 4 in 6) then you also have advantage when making those checks.

Is That It?

Use Shadowdark's stat modifiers instead of B/X ability score bonuses, don't add your Con mod to your hit point rolls after level 1, variable weapon damage is a go. You're using B/X classes so use B/X casting and spells, adjust ranges as necessary to the closest Shadowdark range band. You may or may not use the race options from Shadowdark with B/X classes, I vote 'no' but it shouldn't matter; Humans can just pick a talent table to roll on. Am I missing anything? Let me know in the comments or @ me on the Arcane Library discord server.