Any general thoughts/approaches on scaling up an AD&D campaign to 3.5?

[Saintheart]

Like it says on the can. Because I'm nostalgic and Pool of Radiance was my introduction to Dungeons and Dragons, I'm exploring updating its tabletop equivalent, FRCS1: Ruins of Adventure (https://forgottenrealms.fandom.com/wiki/Ruins_of_Adventure) to third edition and running it for a group of players.

Anyone got any general thoughts or approaches on how you update a 2nd edition module to 3rd edition? The monsters involved aren't likely to be very far from bog-standard, but is it as straightforwards as swapping out the 2nd ed stats for 3rd ed, or does the game play a lot differently?

[Silly Name]

A lot of the differences between AD&D and 3rd edition come up only when stuff starts to stack. While in general a 3rd edition PC will be better than its 2nd edition counterpart, at levels 1 through 3 the difference isn't all that pronounced - they can do some more stuff, hit a bit better and have slightly higher defenses, but most characters are still fragile enough that an unlucky roll can kill them or bring them real close to death, barring some cheesy tricks.

Once powerful spells mixed with more slots and magic items start entering the equation, plus some of the stuff PrCs and feats can do, then you'll notice that 3.5 PCs can deal with mostly everything that gives trouble to a 2nd edition party of equal level (save bullcrap instadeath, no save traps and the like). But even then, supposing your players aren't optimizers, the adventure should be easily convertible and still offer some challenge. You may want to up a monster's damage, adjust DCs and the like every once in a while, but it shouldn't be too troublesome.

[nedz]

The biggest change is with multi-classed characters — so NPCs may take a lot of re-working.

Actually all NPCs are going to require rewriting. In AD&D I could create a stat block for a fighter by eye, but now I have to choose feats, assign skill points etc. Casters are only slightly more work than before.

WotC did publish a conversion handbook, which you can probably find online, but it was quite laughable in th8is regard.

Monsters should be easy - just look up the new stat blocks in the relevant book - but a few have changed considerably. I don't know the module you are looking at so I can't say if this is important, but some of the changes could invalidate several encounters, or possibly even the module itself.

[Efrate]

One of the biggest differences is monster HP is a LOT higher as you go up the CR ladder. Hp bloat is one of the things that makes blasting bad. Between 5 MMs, 6 counting the online one semi preserved on the site, and fiend folio, the monsters likely are in 3.5. Finding them might be hard and they might change enough that what made them great now makes them fodder which might require flexing your DM muscles.

[tiercel]

Illusions are... different. In 2e, in general you have to make and state an active attempt to disbelieve an illusion (which takes an action), and illusions behave more like 3.x Illusion (Shadow) effects, i.e. if you don’t disbelieve an illusion then you tend to treat it as real. (It’s... messy.)

More generally, spellcasters are squishier. 2e casters typically don’t get the full array of defenses that 3.X optimizers may be used to, but in particular they are much more vulnerable than their 3e counterparts to having their magic disrupted:

During the round in which the spell is cast, the caster cannot move to dodge attacks. Therefore, no AC benefit from Dexterity is gained by spellcasters while casting spells. Furthermore, if the spellcaster is struck by a weapon or fails to make a saving throw before the spell is cast, the caster’s concentration is disrupted. The spell is lost in a fizzle of useless energy and is wiped clean from the memory of the caster until it can be rememorized.


No Concentration check for you! Anyone who beats your initiative (and there are several optional subsystems—yay—which can include casting times) can ruin your spell, no readied action required. (This is a reason stoneskin played a lot differently in 2e than 3e.)

[Addendum] Spell Resistance was a lot more hardcore in 2e as well. If something had 90% Spell Resistance, it had a 90% chance to ignore any magical effect that affected it directly. Period. Do not assay spell resistance, do not Spell Penetration, do not pass Go, do not collect 200gp.

[Thane of Fife]

First of all, note that Ruins of Adventure is a 1st edition adventure, not a 2nd edition one.

In general with a conversion from AD&D to 3e, I would note that 3e characters are almost certainly more powerful than 1e characters, and that, in 1e, experience points are mostly gained for finding treasure rather than defeating monsters. So, even more than just because of the differences between editions, experience balances will almost certainly be out of whack if you convert directly. 1e also tends to assume that the party will have hangers-on - hired warriors, sidekicks, and so forth. There are lots of opportunities in the module for the party to recruit such. The module does love to use huge numbers of low level humanoid enemies.

Actual monster conversions should be easy - almost everything in Ruins of Adventure is an SRD monster. There are some exceptions, but not many, and where they exist, they should still be relatively easy enemies to find. For NPCs, it will help you if you understand 1e stat block parlance. For example, this is a stat block for a random character in the adventure:

[Name left unstated]: 10th-level human wizard; AC 5; MV 12"; hp 34; S 10 I 18 W 13 D 17 Cn 17 Ch 10; #AT 1; Dmg 1-4; THAC0 19; AL CE; [Name] carries a wand of paralyzation with three charges, two potions of healing, a potion of speed, bracers of defense AC 5, and a Quall's Feather Token of a swan boat
Spells:
1st level: affect normal fires, magic missile, protection from good, spider climb
2nd level: detect invisibility, invisibility, locate object, wizard lock
3rd level: fly, lightning bolt, water breathing
4th level: polymorph other, polymorph self
5th level: teleport (x2)


However, Ruins of Adventure is a very lightly detailed book. While I have not run it personally, my opinion from reading it is that even if you were running it in 1e you would have to do a lot of work. The above is one of the most detailed stat blocks in the book. In other places, you get

Dwarf, chain and shield, war hammer +1

In some ways, this might actually make your conversion easier.

And the adventures themselves do not cover the full campaign. Rather, they're more like big set piece areas that can form major missions between bits of exploring the city. But the adventure doesn't give you any of the city (besides some generic, unkeyed maps) outside of these areas. So you will still need to make up a lot of adventure to flesh things out and give the party experience (the book does have lots of random encounter tables, but you will probably want more interesting things than that). For example, one of the first encounters described in the book, in the first area the party is directed to, is with 35 orcs and 15 hobgoblins, all at once. That is almost a sure TPK for a first level party. If they hire a bunch of people to come with them, they might be able to get through it.