How hard would it be to convert DnD 2nd edition to a OGL/Pathfinder game?

[Andrek79]

D&D Waterdeep: Dungeon of the Mad Mage is a game one of my best friends really has wanted to play for years. He started to DM it, and never could keep us all on track during Highschool. He gave up being a DM as a result of all our shenanigans LoL

He does love to play with us still & I have considered a revisit now that I see it on FG here: https://www.fantasygrounds.com/store...id=WOTC5EDOTMM

I am wondering as an decently experienced GM that focuses more on story than technicalities, would this be easy enough to plug & play with most of the monsters they could encounter in that old THAC0 based system (adjusting for anything that did change too much for challenge ratings), or would this take a couple months of effort to do a total conversion & only the map & basic story arcs would still apply? There are many traps & secrets throughout the dungeon as well that would likely need to be adjusted.

[damned]

Use the Universal Modules extension.
Maps and story will all work.

Monsters/Encounters/Items would all need to be replaced.

[Corun]

Traps from AD&D? Total conversion.
Loot? Hardest part of conversion IMO. Total conversion of magic items and in generally how much there is. The later can be important as to not increase martial/caster disparity, and CR system was built with expectation of big 6 magic items(cloak of resistance, ring of protection, amulet of nat. armor, belt/headband of str/con/dex/int/wis/cha etc..., +X weapons/armor) being present. Add those to loot or purchase or use automatic bonus progression and reduce wealth accordingly. Probably you should take treasure by encounter table, pool some encounters together and create new treasure from that. Tables from Ultimate Equipment(ready-made roller on official wiki https://aonprd.com/RandomItemGenerator.aspx) can help you with spending this budget in less important rooms. You download fan made modules with items, then quickly throw together parcels.

Monsters from AD&D? Total conversion, but probably was done already in some bestiary or splat book or monster manual(3.5 - add a feat per 3 hd and they will be fine, or substract 1 from cr. There is conversion guide). Check out community extensions/module threads here and in 3.5 - there is a lot of filled stuff. Don't focus on having exact same monsters and reskin a lot. There is extension which parses statblock to monsters - can be quite useful.

Ah, also player expectations about difficulty will probably be different. Searching/finding traps outside of thieves skills in particular, but I am not sure how AD&D2 approached search checks. General deadliness too is approached differently. Infinite cantrips like detect magic, or create water might change a lot.

I personally would just use AD&D2e or Old School Essentials(great, clean rules, but less support on FG, there is thread though) or Advanced Labyrinth Lord or just any retro clone. You will be able to skip conversion effort completely and just play.

[celestian]

I find it much easier to convert 5e to AD&D than the other way round. For the most part just replace monsters from 5e with 2e counter part. Same for treasure. Outside of that would need to be addressed on a per item basis.

[damned]

I really dont think its that hard. Place similar monsters. If they are too tough reduce their number or their HP or their number of attacks. And vice versa increase where needed.

[celestian]

I find it much easier to convert 5e to AD&D than the other way round. For the most part just replace monsters from 5e with 2e counter part. Same for treasure. Outside of that would need to be addressed on a per item basis.

So, I mis-read the subject here. I'm gathering he wants to convert a 2E to a 3E game... that... is out of my purview and I expect more complicated.

[Kelrugem]

So, I mis-read the subject here. I'm gathering he wants to convert a 2E to a 3E game... that... is out of my purview and I expect more complicated.

Actually, there is a conversion manual: https://www.drivethrurpg.com/product...n-Manual-2e-3e (and in WotC's archive it is also somewhere) Not sure how good it is, but it looks elaborated (not just four/five pages speaking about the change of philosophy of the rulesets behind the rules )

[schwai]

Use the Universal Modules extension.
Maps and story will all work.

Monsters/Encounters/Items would all need to be replaced.

I used the universal mod to convert B2 - Keep on the Borderlands to Pathfinder 1e. It took a fair amount of time, but we have been in the module for 5 months and enjoying it plus the side quests I added. The biggest time was altering the encounters and gutting the treasure. Since I customized the treasure, I didn't find that to be too bad. Building up NPCs took more time than anything else. Monsters you might need to sub out and rebalance encounters with the number of foes. The CR calculation tool on the encounter tab is very helpful to get this done quickly. Just plan to do the conversion over a few days if not a week. I didn't do everything at once and I was still converting for more than that, but I changed a few encounters based on the early events in the module.

[Trenloe]

So, I mis-read the subject here. I'm gathering he wants to convert a 2E to a 3E game... that... is out of my purview and I expect more complicated.

I think there's quite a bit of confusion in the OP. The title mentions converting AD&D 2nd Edition to OGL/Pathfinder. The Dungeon of the Mad Mad module linked is for D&D 5th Edition - probably unaware that it's not the 2E version they remember.

So, maybe the best approach, if wanting to run that linked 5E Dungeon of the Mad Mage would be to run it as D&D 5E?