I have been thinking about how combat works in Dungeons & Dragons 5e, and – as with many modern versions of the game – it is no longer a game of attrition. In the early editions of the game, healing magic was hard to come by. (A seventh-level cleric in AD&D with a 16 Wisdom can heal at most 7d8+1 hit points per day). And so, a fight where you lost ten hit points was significant.

In editions of D&D since 3E, healing has been a lot more prevalent. More character classes have healing capabilities, there is greater access to healing magic items (wands of cure light wounds in 3E, potions of healing in 5E), and short-rests restore hitpoints. While there is still a limit to how much you can heal each day, the increased healing significantly affects the game. In particular, scenarios expect that you begin each fight with your maximum hit points.

As such, the pacing of combat has changed. And it leads me to this theory on what makes for exciting battles:

Combat in 5E is a race – can you reduce the monster to 0 hit points before they reduce you to 0 hit points?

It is also a race that is typically over in about four rounds. I have had combats last over ten rounds, but they are rare and usually involve other groups of monsters entering the fray.

Boring races – and boring combats – tend to be ones that one side has no chance of winning. This is especially true when they take forever to resolve. A monster that takes ten rounds to kill but never threatens the characters? That is not that enjoyable to play through.

Easy combats, where the monsters only take a round or two to defeat, are still valuable. They help with pacing and allow the players to feel competent. If every combat is life-or-death, the game becomes stressful, and the characters do not feel heroic.

While D&D is less about the attrition of hit points these days, it still has a significant component relating to other resources’ attrition. A fireball you cast now is one you do not have later. Hit dice run out. So do consumable magic items.

At some point, I need to properly analyse the expected damage of monsters and characters at various levels; it may help us understand the charts for determining Challenge Ratings in the DMG!

Last night, my players fought several skeletal creatures. Each of these creatures was vulnerable to bludgeoning damage. As I was creating new monsters (or reskinning old ones), I increased the hit points of each by about 50%. The combats were exciting – and challenging.

Vulnerability is an odd feature to analyse. At the table, it is either incredibly significant or doesn’t matter at all. As a result, it is challenging to balance in monster design. What vulnerability often says is, “There is a trick to defeating this monster easily.”

Because vulnerability affects how quickly a monster loses hit points, if you wanted monsters to reach 0 hit points at the same rate, then you need to increase the monster’s hit points. How much? It depends on how many characters can take advantage of it!

If all the characters could take advantage, increase the hit points by 100%. If only one of four characters could take advantage, increasing by 25% would keep the challenge level constant.

So, how do you use vulnerability? Here are a few scenarios:

• If the players can figure out the vulnerability, the battle goes from standard to easy difficulty
• If the players can figure out the vulnerability, the fight goes from deadly to standard difficulty
• To allow some player characters to shine with their special attacks

By varying the creature’s hit points, we can change these situations around. A monster with 200% of regular hit points but a vulnerability that everyone can exploit goes from being deadly to standard. A creature with average hitpoints but a vulnerability that everyone can exploit goes from standard to easy.

If two of four characters can exploit the vulnerability, you could give the monster 125% of its HPs. This is less than the full potential, so if the two PCs figure it out, it is like it had… err… 80% of its hit points? Something like that! At this point, the monster is slightly more challenging if the characters don’t figure out the vulnerability and slightly easier if they do.

However, all of these situations assume that the characters (a) need to figure out the vulnerability and (b) have the means of exploiting that vulnerability.

For a creature that is vulnerable to fire, it is exceedingly likely that the vulnerability will be known after the first set of attacks (caster with firebolt). If a creature is vulnerable to acid, then it might be several combats before the players find out – if ever. Which, of course, bring forth the possibility of research. (This monster is deadly plus 200% hit points, how do we defeat it?) When a monster seems impossible to defeat, working out a trick to defeat it is great – especially if every member of the group can use that technique.

The fewer people who can benefit from the vulnerability, the more you should use it as a reward for those players rather than a puzzle to solve.

Those are a few of my thoughts based on recent play (and some tweets from ThinkingDM). I may dive further into vulnerabilities in future; they are an interesting design tool.