Monsters on a Role: Lurkers

Talk about an unbalanced encounter!

Next up in our series examining the roles monsters can play on the battlefield, we have the lurker. This one is going to have a good bit of setup, but the payoff is amazing. Last week, we discussed a "roguish" type of monster, the Skirmisher, but we really only covered half the rogue. The skirmisher is all about getting through the PC's front line and dealing damage to their squishy types.

The other half of the rogue is the sneaky kind. And that's what we'll discuss for the Lurker.

Lurkers

Lurkers have a slew of modifications that are going to require an understanding of CR adjustment, Trait creation, and combat design. You can now see why I've been discussing that in previous articles, because it's been leading up to this guy (and even more next week).

Lurkers have the following traits:

• Low HP
• The ability to boost defenses for a round (including stealth)
• The ability to boost attack bonus and damage for a round after their defensive round

Now, that sounds like a lot, but there are actually quite a few lurkers in the MM already. We can use them as inspiration.



ExcuseMeHaveYouHeardTheGoodWord?

First off, the easy part. We already discussed the impact of lowering HP as opposed to raising it, and the same applies here. The formula again:

Effective HP increase/decrease / 30 = Increase/decrease in CR

Lowering the monster's HP gives us some wiggle room to increase the CR back up to full, but it also does something important to the flow of combat.

The idea behind a lurker is that, for one round, they are both untouchable and horribly deadly, the embodiment of a trap going off on the battlefield. Before that round, we want them to be hidden or well-defended, but after, they need to die quickly.

This is a monster that is going to change the flow of combat. Suddenly, the fighter is down to under half their hit points. Suddenly, the wizard is unconscious. Now the support team needs to act, or the strategy needs to change.

But after that crucial moment, we want our monster to go away. Why? Because if the monster pulls off another round like that, you risk decimating the PC's strategy instead of changing it. The group needs to be challenged, not obliterated.

So, lowering the monster's HP not only solves our combat dilemma, but allows the players to take revenge for the killer blow in mid-combat. It adds to strategy and narrative.

Now that the HP of our Lurker is sufficiently lowered, how do we get that CR back up? Let's talk traits. We'll need two: one defensive and one offensive.

Defensive Traits

It believes if it can't see you, you can't see it

When looking at defensive traits, we are looking for something that will allow the Lurker to get into attack range safely. After they are within range, this trait should go away.

The classic Lurker tactic isn't even a trait: They simply hide. While hidden, they give disadvantage to any attacks made against them. From the trait "Nimble Escape" (DMG pg. 281) we can see that hiding every round is the same as an AC boost of 4. Remember our AC formula:

• If CR is above 1, AC increase/decrease / 4 = Increase/decrease in CR
• If CR is less than 1, AC increase/decrease /8 = Increase/decrease in CR

So this will increase CR by 1 at high levels or by 1/2 at lower levels.

Now, a quick aside: If Nimble Escape increases CR by 1/2 (at least!), then how are goblins CR 1/4?

Well, the designers didn't expect the goblins to be hiding every round. In fact, very few DMs will have monsters hide once they are in combat. Thus, the lower CR. But our Lurker is different. We want them to be engaged with the enemy while hiding, and that effect will matter.

The next good defensive traits aren't even really considered defensive: False Appearance and Aggressive.



"The mimic uses its Fist spell"

How are these good for Lurkers? Simply put, they allow a creature to be not considered a target until the round they deal damage. Then, either by running in or revealing themselves, they surprise the PCs and deal their damage. There are some fun variations on this as well: dive-bombing fliers, using foggy terrain, enemies hiding in crates, etc.

Does this have an effect on CR? We know that Aggressive has a minimal effect, and False Appearance (DMG pg. 280) has no effect. Why?

I think it's because the designers assumed that any creature with a False Appearance or Aggressive would use it in the first rounds of combat, then it'd be over. The suit of armor is alive, the stalagmite is a roper, etc etc. So what do we need to adjust for our Lurker, who will be waiting a few rounds before engaging?

Actually, nothing. Think of it this way: the creature is essentially a reinforcement. When a creature is added to a combat in later rounds, we don't adjust the CR of the encounter. Now, whether or now we should is another technical debate, but I believe that latecomers should get the full benefit of their CR. So even though our lurker is hiding a few rounds, we are basically saying that they will die in round 3 instead of round 1.

This is another reason why the low HP is important: it keeps the combat length reasonable, even when an additional foe is added halfway through.



Perfect for when your players won't leave the tavern

Now, there's a few more ways that a Lurker can act defensively. If running into range or hiding isn't possible, then we need something to protect the Lurker while they get into position for their attack. There are tons of possibilities here, so I'll name a few:

• Blur (PBH pg. 219)
• The Dodge action (PHB pg. 192)
• Blink (PHB pg. 219)
• Ethereal Jaunt from the Phase Spider (MM pg. 334)
• Invisibility (PHB pg. 254)
• Shield (PHB pg. 275)
• Stoneskin (PHB pg. 278)
• The Flail Snail's Shell Defense (VGtM pg. 144)
• The Doppelganger's Shapechanger (MM pg. 82)

Essentially, anything that provides a round of increased AC, Damage resistance, disappearance, or disadvantage for a round. These abilities in some form are actually very common in the MM, which is why I said earlier that there are lots of good Lurkers in the game already.

The CR effects of each of these abilities is fairly easy to calculate, now that we've laid the groundwork for defensive adjustments. Just remember: disadvantage is the same as +4 AC, entering combat late has no CR ramifications, and apply the CR to AC modification formula above.

I do want to talk about damage resistances quickly before we get into the offensive traits. Damage resistance is another area where CR effect changes at higher levels, as the party picks up more weapons and different spells. Stoneskin would be impenetrable to a low-level party, but a high-level party would laugh it off.

So, to apply damage resistance, we adjust the Effective HP the monster has and plug it into our HP formula (above). The table changes if the damage is simply a resistance or a full immunity.

So, using the formula, the Stoneskin spell has the following effect on CR:

• CR 1-4: CR increases by the creature's HP / 30
• CR 5-10: CR increases by the creature's HP / 60
• CR 11-16: CR increases by the creature's HP / 120
• CR 17+: No effect

If you're savvy, you can see how this will effect low-CR monster in a big way, possibly pushing them into higher CR categories. And yes, that means the formula will change again.

Offensive Traits



He's just trying to save him from that garish helmet

Now, for offensive traits, we have two goals: to increase attack bonus and damage for a single round.

Many of these traits function offensively the same way that the defensive traits work. For example, advantage grants +4 attack bonus. But we haven't discussed a formula for attack bonus yet! Well, here it is:

• If CR is above 1, Attack bonus increase/decrease / 4 = Increase/decrease in CR
• If CR is less than 1, Attack bonus increase/decrease /8 = Increase/decrease in CR

That should look pretty familiar.

Our offensive traits for increasing attack bonus are pretty straightforward now. Find an ability that increases attack bonus, figure in the CR adjustment, and move along. I think advantage on the attack is the easiest way to go, but don't discount giving cool accuracy-boosting abilities to monsters, like the War Priest's Guided Strike (VGtM pg. 218).

Now comes the trickier part: we need to add some damage to this single round. Now it seems like we can just use our damage formula, but there's something else I want to address.

Damage Increase/decrease per Round / 12 = Increase/decrease in CR

This formula is built on the idea that the damage done each round is consistent. That won't be the case with our Lurker. According to the DMG (pg. 278), if the damage done each round is inconsistent, we need to take the average damage of three rounds and use that instead.

So if we gave our Lurker a poisoned or magical weapon, we'd account for the full amount of increased damage. But we don't necessarily want to give the Lurker a special magic weapon, since that means the damage could be used in subsequent rounds, which would be bad. We want a one-shot big hit.

I'm "sneaking"!

Instead, let's look at ways to increase a single round of damage: spells, sneak attacks, and the Pounce ability (DMG pg. 281).

Note that I'm avoiding the Surprise Attack feature. That's only because it has to activate on the first round of combat, which isn't when our Lurker will be most effective.

So for each of those abilities, the DMG tells us to increase the damage output for a single round by the amount listed in the trait. Then, we take the average of the three rounds.

I think you can start to see why this is a big deal. When we calculate the amount of damage our lurker can deal, we have to use a modified formula. This allows us to give a lot more damage with a lot less CR impact.

Damage Increase/decrease of offensive ability / 36 = Increase/decrease in CR

So we could add a sneak attack or pounce trait that deals 36 (8d8) damage, and only increase the CR by 1. That's like giving a monster the ability to cast Blight!

Of course, it's only for one round, which is why it works. But with that in mind, we can start looking at damage in a new way.



I'd take the dodge action

That was a big article. Let's finish off by building a couple Lurkers! I'm using kobolds of course, and keeping one mundane and one magical.

For our mundane lurker, let's go with Kobold-In-A-Box! How did he get in the box? Easy - the crate is actually covering a tunnel, and when combat started he crawled up under the crate, ready to burst out. So he'll be in position by round 3, which is his defensive ability - he won't be targeted until that crate busts open.

We can also give him an ability that grants advantage on attacks when he leaps out from hiding: Ambusher! We'll just adjust the ability so it works on non-surprised creatures. Finally, let's give him Sneak Attack as well, and add a hefty 7 (2d6) damage to that strike.

Finally, let's drop him to 1 HP. That way, after his single attack, the party can wipe him out and get back to fighting.

So by my calculations, all of that bumps his CR up to just under 1, which I would round up to 1. That actually feels right - a sudden 11 damage would add a lot of danger to a level 1 or 2 party, but above that he'd be more of the game-changing threat we could expect. Do your own math and see if you can get to the number I got!

For our magic kobold, let's create a stronger variety of lurker. First off, we'll use Blur to defend. That's +4 AC. Then, let's go full-out and say this Kobold is a Warlock of an Eldritch Being, and can cast Blight. Since at that level, 5 HP is really nothing, we don't have to adjust the HP to make this beastie killable in one hit.

So how do we make Blight have a higher attack bonus? Well, we can give disadvantage on the save. Here's a hint: I'm treating it exactly the same as an increase in attack bonus. We'll cover that more next week.

So in the end, I have a CR calculation of 2 1/8, which I'll round down to 2. That's a pretty hefty little Kobold!

Hopefully these monster roles are giving you ways to keep your combats interesting. I wouldn't recommend pitting the Kobold-In-A-Box against a group of level 1 PCs the way you would do with a similar CR 1 creature. Rather, the Lurker adds something to a bigger, higher-level combat, and keeps it from becoming stagnant.

Perfectly reasonable!

Next week, we'll be talking about the Controller, which is an amazing to make your combats dynamic and interesting.

Thanks for reading!