Easily Convert Old D&D Adventures to Fifth Edition
The first Dungeons & Dragons adventures were published in the mid-1970s, and a steady stream of material followed over the next forty years. With the advent of Fifth Edition in 2013, this stream became a firehose, with thousands upon thousands of new adventures added in just a few short years.
Why Convert Old Adventures?
Given the super-abundance of Fifth-Edition compatible material, you might wonder why anyone would bother trying to convert the adventure modules from older editions. I can think of three reasons:
Some of the old adventures are superb. Products such as Pharoah, Dark Tower, and The Lost City will provide your group with hours of gaming delight. In 2004, WOTC released a list of The 30 Greatest D&D Adventures of All Time. It is well worth perusing.
Sometimes an old adventure fits your needs perfectly. In my current campaign, I needed some monster-filled caverns set far beneath the city of Calimport. I thought about creating something new, then realized that the old classic, The Lost Caverns of Tsojcanth, was precisely what I needed.
The old adventures fill a neglected play duration. These days, the official WOTC books contain full campaigns that you could easily spend a year running. By contrast, you can complete most of the indie-5e and Adventurer's League material in only 1 or 2 sessions. The old 32-page and 64-page adventure modules from TSR occupy a useful middle-ground.
Converting to Fifth Edition
Having established the why, we need to look at the how. WOTC has released some official guidance on adventure conversions, but I believe it over-complicates things. The following quick-and-dirty approach has worked very well for me, and I'm confident it retains the "feel" of old adventures just as well as more detailed guidelines.
There are only two things that need converting - treasure and monsters. You can usually run tricks, traps, puzzles, and social encounters as written in the original, with a bit of on-the-fly massaging.
Treasure
Adventures written before Third Edition tend to hand out a lot of treasure, partly because this was the primary means of awarding experience points. For these adventures, I recommend you halve the treasure awarded. For Third and Fourth Edition, you can keep the treasure the same.
Regarding magic items, I suggest you hand out as many as are indicated in the adventure text, regardless of edition. Choose the closest matching item you can find in the Fifth Edition Dungeon Masters Guide, but don't exceed the rarity indicated by this chart:
Tier 1 - Uncommon
Tier 2 - Rare
Tier 3 - Very rare
Tier 4 - Legendary
For example, your characters are level 6 and come across a sword +3. Since that is very rare, you should substitute it for a sword +2, which is only rare. If there is no good matching item in the DMG, choose a substitute.
Monsters
You can also do monster conversions easily using the Lazy Encounter Benchmark developed by my friend, Mike Shea. This guideline says:
An encounter may be deadly if the total of monster challenge ratings (CR) is greater than one-quarter of the total character levels, or one-half the total character levels if they are above 4th level.
Ok, you might need to read that a couple of times, but it's straightforward in practice. My current party has six characters, all at level 6. Following the guideline, I sum up the character levels and get 36, then halve that number to get 18. Accordingly, if the total monster CRs for an encounter is 18 or less, it is probably ok for my party. I should note that I have an addendum to the Lazy Benchmark: the CR for any single monster should not be more than twice the average party level.
With this guideline in place, substitute the monsters in the old adventure text with the equivalent monster from Fifth Edition. So long as you don't exceed the CR threshold calculated above, you are fine. Don't worry if a fight is too easy; you just want to make sure you don't throw anything excessively hard at the party.
Here's an example. The party I described above is traveling through S4 The Lost Caverns of Tsojcanth when they meet a clay golem. The Fifth Edition monster manual has a clay golem with a CR of 9. Since this is less than the CR threshold of 18 I calculated above, I can use the Fifth Edition clay golem in this encounter.
What do you do if, having switched to the Fifth Edition version, the total monster CR exceeds your CR threshold? If the encounter involves multiple monsters, remove some of them to bring you under the CR threshold. If it is a single monster, my preference is to keep the monster but give it the minimum hit points prescribed in the stat block.
Ok, what if there is no equivalent monster in Fifth Edition? In that case, I substitute a similar creature. For example, Tsojcanth has a cave full of mobats, which are like giant super-bats. There are no stats for these in Fifth Edition, so I just used the statistics for another flying creature, griffons. It worked fine!
Let's look at another example. Khyber's Harvest is a Fourth Edition adventure for second-level characters. One of the first fights is against 2 cultist eyeblades and 2 orc wardens. These monsters don't exist in Fifth Edition, so I would just substitute them with 2 cultists and 2 orcs, which do have statistics in Fifth Edition. Then, check the challenge rating using the Lazy Benchmark, and we are good to go.
Go Forth and Convert
That's it - that's the method. I told you it was easy! If it seems over-obvious, I can only assure you that I've used this approach in play and that it works. I hope this article encourages some of you to start exploring the rich legacy of older D&D adventures.