How can I convert enemies from D&D 3.5e to 5e?

Question

I'm trying to convert The Forgotten Forge from the back of the Eberron book into 5th Edition to run it, and right now I'm trying to get the enemies inside it converted over, using the UA article as a guide in some places. However, a big sticking point I'm finding is getting the enemies properly converted into 5e's rules. I've found a few guides (like 3.5 to 5E simple conversion guidelines) but all of their methods for converting hit points leaves the monster with far too few hit points as far as I'm concerned.

For example, a CR 2 creature from the adventure (the Warforged Rogue on pg. 312, if anyone has the book) got converted over with only 18 hit points, and all the guides I'm finding seem to say that's correct. However all other CR 2 creatures I've looked at in 5e books have far more hit points, and CR 1 creatures tend to have more hit points than that. For comparison, the Goblin Boss, a CR 1 from the MM, has 21 hit points. Am I doing something wrong? Am I wrongly expecting the CR to convert over a little more directly?

To be clear, what I am asking for is a way to convert a CR 2 creature from 3E into a CR 2 creature from 5E. The DMG almost helps, but the hitpoints it lists seem too high.

Answer 1

Wizards of the Coast posted a short 4 page article about conversion from previous editions of D&D to 5th edition. It covers monsters as well. You may even convert those from 1st or 2nd edition. I find it quite helpful.

Conversions to 5th Edition D&D:

Quick Conversion

In third edition, you can use monster statistics included in an adventure as a guide. Monster distribution in this edition is fairly close to the distribution in fifth edition. As in earlier editions, such creatures often deal lower damage and have fewer hit points than their fifth edition counterparts. Most statistics in third edition include the creature’s ability scores. Use the following parameters:

• Armor Class can be an average of touch AC and actual AC, or 20 percent lower than in third edition. The upper limit is 22.
• Attack roll modifiers are the appropriate ability score modifier + 3.
• Saving throw DCs are 10 + the appropriate ability score modifier.
• If a creature has to make a check or saving throw, use its ability score modifiers. Grant it a +3 bonus if it should be good at the roll.

Careful conversion

In older adventures, you’ll sometimes run across creatures that lack a published equivalent in fifth edition. In this case, the “Creating a Monster” section in chapter 9 of the Dungeon Master’s Guide is your best tool. The “For the DM: Race Conversions” section in this document can also be helpful.

If you choose to create the monster whole cloth, start by replicating the original monster as closely as possible using elements from fifth edition. Use the HD as the creature’s HD in fifth edition (the level of a fourth edition monster can determine the number of HD it has). Ability scores should be in the fifth edition range, from 3 to 30; third and fourth edition ability scores often need to be reduced. For special traits and attacks, use existing creatures as guidelines.

Once you’ve converted a monster to fifth edition or created a new one, you can use the Monster Statistics by Challenge Rating table in the Dungeon Master’s Guide to determine the creature’s challenge rating. Then, you can adjust HD and other statistics to get the challenge rating you desire.

Answer 2

The conversion method listed at the Wizard site under the material UA (Unearthed Arcana) is downloadable and does a great job. In 5e HP is good but it is not the old hack and slash of 1-3.5 editions. When they introduced conditions, it changed HP as a base. Battles can be won or lost from forcing conditions, not necessarily lowering the HP only. Poison, for instance, forces serious penalties while affected (duration is probably the only troublesome area there) as do stunned, prone, etc.. Try an experiment with a group with the lower HP as a training method just to see its effects. Use the conditions. You may find it compensates more heavily.

Answer 3

Not to sound simplistic, but if it doesn't have enough HP you could always increase them based on the HD of other 2 CR monsters you see. Compare the abilities, the 'toughness' of the monster, and so on and ballpark the numbers - when I Dungeon Master it is always better to be flexible than precise. Fudging a number here or there is important in the name of fun; if you accidentally give it too many HP and the battle drags on, or the creature is too powerful - let the PCs down it with their next attack. If it's too weak or quickly dispatched, give it an unexpected "rush" of energy ("This is not even my final form!") by adding another pawful of HP to it. In the name of fun, it is the job of the DM to reconcile rules that are imperfect with players who are unpredictable.

Best of luck to you!