Should I adjust encounter challenge for PCs with damage immunities?

Question

Recently, two of my PCs became afflicted with lycanthropy (of the wererat variety). According to the Monster Manual, characters with lycanthropy acquire the damage immunities of their respective lycanthrope (among other stats). Immunity to bludgeoning, slashing and piercing from nonmagical, non-silvered weapons is a pretty big advantage that isn't otherwise baked into encounter values.

The DMG is pretty mum on this; should I change the experience values of encounters to account for this?* If so, how should I?

And of course, "it's up to the DM" is a preëxisting assumption here. I am the DM and I'm looking for input.

*Note, this is unlikely to actually be necessary in my group, as they have access to remove curse and are most likely going to use it before the next adventure. But it's a valid question that doesn't appear to be answered otherwise.

Answer 1

This is tricky. I'm actually kind of fond of the Monster Manual's suggestion of the PC becoming a DM controlled character if they embrace the curse (at least until it is lifted). Since that's not your original question, let's actually dig around and see if we can't get an answer.

My initial assement is that we need to re-examine the rules presented in the Monster Manual for Lycanthropes. If you'll open your hymnals to page 207, we'll see the green box labelled "Player Characters as Lycanthropes" on it.

The first paragraph reads:

The character gains the lycanthrope's speeds in nonhuman form, damage immunities, traits, and actions that don't involve equipment. The character is proficient with the Lycanthrope's natural attacks, such as its bite or claws, which deal damage as shown in the lycanthrope's statistics. The character can't speak while in animal form.

This actually sounds familiar. If you flip back to the Druid in the Player's Handbook and look up Wildshape, you'll notice that the wording is exactly the same as the Wildshape ability, meaning if we're not embracing the curse, and thereby mastering the shapeshifting, we only have to worry about encounters on the full moon getting adjusted.

So, gut answer says "Nah, you're good." However, let's pretend we're normal PCs and go "Sweet, shapeshift!" and embrace it.

As stated earlier, you do entirely have the option (which I suggest!) of taking control of the alignment-shifted PC until they're healed. That'll solve the problem outright.

However, since we're going to begrudgingly get into mechanics, a Lycanthrope in shifted form (based off a human) runs about 3.5 CR, all told. You can add in their class levels, and we'll call it probably a 5.5 CR when they're shifted (I'm assuming level 2 PCs). So, you're definitely in need of some bump.

This sort of thing is a delicate balancing act in a home game, but your goal is to start tuning your encounters to their level. Go ahead and build each encounter as normal, but count the infected PCs as one step higher than the intended difficulty of the encounter. For example, if your party is 4 level 2s and two have lycanthropy, build the encounter at 500 XP budget — 200 for the uninfected PCs, and 300 for the two infected PCs (150 xp/character is 'hard' for level 2) — and run the encounter. Keep about 100 XP or so of monsters in reserve (this will kick it to Deadly) to show up if things are too easy, but be ready to reduce things the same way (−2 AC from all monsters or −5hp is what you'll need to get the encounter on-the-fly adjusted to dial back the pressure).

You'll need to run a few encounters like this to start tuning the difficulty, and I would recommend as well pushing on the infected PCs' ability to control themselves. Wererats are notoriously klepto, at least in my games, as well as nasty, dirty little creatures. There's a certain point at which they'll get disadvantage on Charisma checks, and another where I think it'd be okay to start disadvantaging their wisdom saves as well if they try to resist what is now their nature.

Don't forget too that people don't like Lycanthropes. There's grave consequences — usually wererat/wolf/what-have-you hunters — who will be looking to find the wererats skulking around town. The PCs are also probably a bit unsettling to be around while they're cursed as well, but those are just secondary thoughts for flavor.

Answer 2

CR calculations aside, this is a question that has a soft answer.

What would be more fun?

If your players are jazzed about being wererats then let them lay waste for a bit, enjoying that newfound immunity. Then you can start to adjust enemies (they start carrying silvered weapons, etc) as word gets out. You can also play up the negative aspects of lycanthropy so players will have to decide whether or not to cure themselves if it means they lose their combat advantages.

Unless the characters are very low level then the damage immunity isn't actually that over-powered, barbarians have resistance if they rage (and if they go the bear route at 3rd level it covers almost ALL damage types) which can help almost as much. So you will probably not have to adjust much for encounters to still feel balanced.

Just remember that intelligent creatures have access to the same methods of defeating wererats that PCs do (silvering weapons, enchanting weapons to be magic, using poison or fire, etc) so your PCs shouldn't feel like they can just stroll into a monster room without fear.

Answer 3

Lycanthropy (if you let them control themselves) is a HUGE power boost for any character. In previous editions there was something called Level Adjustment (LA), which for a lycanthrope meant that they were effectively 2 levels higher than their total class levels. The gist of this is that your level 4 were-rat would level up to 5 when he got enough exp for a non-LA character to get to level 7, and when planning encounters a DM would take their actual level + LA = Effective level, and use it for calculating CR, etc.

In 5e LA was done away with, but the bonuses from lycanthropy remain, so I would deal with them in a similar way. Count them as being 2 levels higher than they actually are when planning encounters.

Note that if some of the party are were-rats and others are not, there will be a large difference in power which could result in the same encounter being trivial to the were-rats, while the 'normal' pcs get one-shot.

Answer 4

No.

There are many ways of dealing with a character that gains lycanthrope, but if you want to allow a low-level character to continue playing a lycanthrope in a party, don't expect encounters to be balanced. The character itself has immunity to nearly all damage that will be done by NPCs at that level. If you make the encounters significantly harder, all that will happen is the regular PCs die while that one lives.

Lycanthropes need special hunting parties to go after them, and this is still true when they're the PCs. Maybe a party of clerics and wizards sets out to destroy the evil. Or maybe it's a group of clerics doing all they can to keep the only fighter in town that has a silvered weapon alive and fighting. Bandits that you encounter will probably run away to save their lives. Peasants in a town might band together in order to tie the monster up.

Once you get into higher levels, it's not so much an issue, but at lower levels, simply throwing harder encounters at the party is not the right answer.