[RPG] Can D&D 5e adventures be converted to AD&D

If using a 1e/OSRIC group with an LotFP adventure, no modifications should be needed. The challenges are often not connected to character stats. The adventures should work equally well with any traditional ruleset.

If using LotFP characters with 1e/OSRIC modules, since those are usually more combat-heavy I would make sure the LotFP characters are one level higher than what the module recommends. For example, if an OSRIC module states it's for adventurers levels 4 - 7, I'd make sure the LotFP group is level 5 - 8.

I would make the same recommendation if using Basic Fantasy, Labyrinth Lord, or Swords & Wizardry characters with a 1e/OSRIC module, because 1e characters are generally built tougher, both due to bigger dice used for hit points and because of greater benefits for higher ability scores and a greater chance of having those higher scores.

Maintaining the AD&D Feel

If you want to maintain the AD&D feel of this module you have to keep the following in mind: it's a death-trap.

I have played it, I have DMed it and I have spoken to many people who fondly remember the way their characters died in it; I have never spoken to anyone who finished it although I and a few others have escaped from it with some of our party still alive.

I suggest you start by telling your players to roll up their characters and a couple of "spares". This should get their mindset right.

The monsters can be swapped out with their 5th edition equivalents; there are very few of them and they are not the major obstacle anyway (except for Acererak; make sure you read the sidebar on him in the Monster Manual).

The traps and tricks could (should) be played pretty much as written; I would allow the use of Wisdom (Perception) or Intelligence (Insight) to detect them and find out how they work respectively but I would be setting DCs at 25 or 30 - this is a module about player skill, not character skill. See discussion on skill checks below.

It rewards slow methodical play where details matter. Let that be your DM style - tell the players everything (relevant and irrelevant), then tell them again, then again, then ask them what they want to do and require them to be precise. An example of how I'd handle a particular challenge:

Off the first corridor there are a sequence of 10x10 foot rooms which each have a secret door leading to the next (with a twist, of course). As written, each of these opens in a specific way. I would play this with say a DC20 Wisdom (Perception) check to find the doors, with advantage for each room after, say, the second because it is clear that there is one in here somewhere! This should be readily achievable for a party of this level. Finding them doesn't tell you how to open them though; I would allow a DC30 Intelligence (Investigation) to find out how to open them - more or less impossible. So, to open them the players have to state what they are doing - sliding up, sliding left, pushing (where?), pulling (where?) etc.

Skill checks

My preference is to reduce but not eliminate the influence of character skill. This is, if you like, a clarification of the advice given on PHB p.178 (my emphasis).

Finding a Hidden Object

When your character searches for a hidden object such as a secret door or a trap, the DM typically asks you to make a Wisdom (Perception) check. Such a check can be used to find hidden details or other information and clues that you might otherwise overlook.

In most cases, you need to describe where you are looking in order for the DM to determine your chance of success. For example, a key is hidden beneath a set of folded clothes in the top drawer of a bureau. If you tell the DM that you pace around the room, looking at the walls and furniture for clues, you have no chance of finding the key, regardless of your Wisdom (Perception) check result. You would have to specify that you were opening the drawers or searching the bureau in order to have any chance of success.

The "might otherwise overlook" is crucial and can be clarified by adding the following to the example:

If you say you open the drawers and remove the clothes then you find the key regardless of your Wisdom (Perception) check result; indeed the check is not needed at all.

In order to do this you need to set DCs that are very hard (DC25) or impossible (DC30); after all, the place was designed by an evil genius who has refined the place over millennia with the benefit of observing countless test subjects try to break it.

How hard is that?

Well, I have made an anydice program to show this. It assumes:

• the party will help the primary character; giving advantage
• the primary character has a score of 20 in the relevant statistic; giving +5
• the primary character is between 9-12 level; giving +4 proficiency bonus or +8 for expertise

It breaks down like this (rounding to nearest %):

\begin{array}{r|lll} \text{} & \text{DC20} & \text{DC25} & \text{DC30} \\ \hline Non-proficient & \text{51%} & \text{10%} & \text{0%} \\ Proficient & \text{75%} & \text{45%} & \text{0%} \\ Expert & \text{91%} & \text{70%} & \text{36%} \\ with Bardic Inspiration & \text{98%} & \text{85%} & \text{60%} \\ \end{array}

Now there are various spells and magic items that could improve this but if the players do this then they are spending scarce resources and they will be that much weaker latter on.

Thanks to @Mala for inspiring this portion of the answer. Please feel free to point out any errors in my assumptions.

Referring back to the example:

A party with a Bard or Rogue with expertise in the relevant skills will find the doors 91% of the time and work out how to open them without experimentation 36% of the time. I could almost be talked into lowering the DC for detection to 15 which gives a 99.75% chance to find; but then, I'm a soft touch.