So the characters  in my campaign are 9th level. One of them is a Circle of the Moon Druid. And it's becoming a problem in terms of creating encounters that are truly challenging (i.e., could result in character death or at least believable threat of it).

The druid has 2 wild shapes a day, with a maximum CR of 3. Doesn't sound like much, does it? But the giant snapping turtle (Beast CR 3) has 75 hit points. If the druid is in the water, they can become a killer whale, with 90 hit points. That's effectively at least 150 bonus hit points before the druid ever loses any of their "real" hit points.

If that same druid takes the polymorph spell, that's 3 potential changes and buffs to hit points. Obviously, this is going to depend on whether the campaign has prehistoric creatures (and which kind). And environment/space limitations can play a role as well. But let's assume this is an environment in which creature size isn't a worry. So let's not even go to maximum CR allowed by the druid's level (9! but there's only one canon Beast that exceeds CR 8), but stick to CR 6 beasts, and not choose something explicitly prehistoric. Take the Huge Giant Crab, which as a CR 6 and 161 hit points.

This means the 9th level Circle of the Moon druid effectively has over 700 hit points, when you take all the shape changes allowed and the druid's own hit points into consideration.

This is insane. How can you possible build encounters for the party that aren't going to be wildly unbalanced? (This doesn't even take into consideration that the party also has a 9th level wizard who also has the possibility of 3 polymorphs per day, providing further hit point buffs upwards of almost 500 total hit points.)

(I don't blame the player, to be clear. They're simply playing the character as the rules allow.)

The only two options I can think of are to use foes with a LOT of dispel magic spells or to make the encounters really unbalanced in terms of either monster hit points and/or damage capabilities. Which ultimately isn't fair to the characters who don't benefit from such abilities, and ultimately makes me feel adversarial with the group, which I'm not thrilled about. Or, worse, a third option, and I just become an XP supply machine for the party, and there's never any real danger to them.

(I've posted this in the Dungeon Master's Only forum because this is, for me, a dilemma about how to run the game, not about a class's rules or abilities. A fine distinction, I'll grant, but it feels more like the former than the latter.)

The big weakness of moon druid wild shape is... sure, there's a lot of hit points to grind through (I don't have the book the Giant Snapping Turtle is in, but there's other CR 3 beasts), but they tend to have both lousy AC (so it's not as hard to get through those hit points as you might think) and lousy attacks (low accuracy and not much damage). This usually means "ignore the moon druid while beating everything else up, then surround and pound".

As for polymorph, you can break concentration far faster than grinding through the hit points.

Providing differing terrain and a vertically dynamic opposition might provide some of the challenge that you seek. If the opponent has the ability to fly, the party would have to bring it to ground, or go and meet it in the air. If that same opponent were able to swim, uses of wildshape and polymorph might be used up quickly. Including some spaces that are too small for your Wildshaped Druid to fit through could also create a pause in their tactics.  Terrain that traps, or constrains the size, mobility and ability of the intended party is desirable high ground.

Using conditions like Prone and Exhaustion work well to challenge foes, as does a spell like levitate, as it removes a creatures movement speed, unless they can fly. Sickening Radiance can become problematic if the party doesn't react to it well.

If your party is expending resources, they are meeting a challenge. If you feel that those challenges are trivial, add more. If you make them more challenging (lethal), as you have pointed out, they get swingy. Aiming your encounters solely at the PCs hit point pool isn't fun. Shadows can kill a 500 hp behemoth without getting to the bottom of that HP pool. Unconscious creatures underwater can drown, unless they innately (or magically) have water breathing.

It's also worth mentioning that level 9 is when all casters start to get access to some really powerful spells and abilities. If you have a lot of martials or multiclassed characters in the party, that boost can feel even more disproportionate. Druids in particular, especially moon druids, are a strong class in comparison to most, so it's no wonder you're feeling the tension.

At this level and higher, casters will start making a lot of things trivial. The kinds of obstacles that challenged them even at level 8 won't phase them anymore. It's a learning curve on the DM's part to identify how they're operating as a team and how you can challenge that.

If they're using the druid as a meat shield, maybe you throw multiple enemies on the map that will go after the squishies, forcing the druid to decide whom to protect. If the druid has an HP pool that you can't deplete well, maybe you start adding monsters who are scary because they petrify or paralyze - the danger isn't a bite attack, it's getting sidelined. If the party is really mobile, maybe you introduce some monsters that take advantage of incorporeal movement and hit-and-run tactics - harder to kill something you can't reach or see. If you really do want to burn through HP, maybe your monsters take advantage of natural hazards (lava, acid pits, fire) that deal ongoing damage per round unless the PCs use their actions to save themselves. 

Upper tier 2+ play is a new ballgame because you have to rethink your challenge strategy more frequently. Once you identify what tactics you've been relying on and what the party is good at, you'll have a better idea of how to give them the workout you're looking for. 

Yeah, I'd say environment is the key here. It's real easy to end up with a relatively flat encounter environment, but scattering cover and some environmental features that offer height can work for the enemies just as well as the players. 

That said, I'd argue that one of the things we're doing is laying out the obstacle course for our players to work their way through, around, under, across, or ignore entirely. The real question is in why you're laying out that encounter though.

For example, let's set up an encounter in a warehouse, barn or other similar indoor space. In that space are littered crates, barrels, walkways, and several rows of cages with canvas draped over them. Inside the cages are mountain lions or something similar. Those lions are being sold to the highest bidder tonight to be skinned and used as commodities. Any half engaged druid (and a good chunk of nature loving rangers) are going to need to see these creatures freed...especially when they see one of the warehouse staff abusing one of the animals. 

Now in this situation let's say you've got a Fighter, Warlock, Druid, Sorcerer, and Ranger all level 6-8. You've also got six guards, let's give them stat blocks of the Drow Elite Warriors because we want them to have a challenge. You've also got one big boss overseeing the operation, and perhaps a few commoners and dock workers...perhaps even some town guard in the area. Then mix in that each lion freed is likely to become aggressive on a failed animal handling check (for anyone choosing to release the lions). You've got a lot of different enemies here and frankly in this scenario your Druid is going to be vulnerable while they try to free the animals. These cages, as they are Steel are going to have an AC of at least 19, and I'd stack them with 30-40hp before you can actively break them. This presents a real challenge depending on how you set it up.

Now, maybe your druid isn't nature loving...though in that case, I'd question their desire to play as a druid...but hopefully you take the point of that example. It's about finding what is going to make your druid want to either not wild shape, or even better, drop their wildshape outside of combat. Seeing druids wildshape outside of combat is always a joy...it means they've got one less wildshape per day. 


As to the Polymorph spell...I do tend to rule that players can only choose from the beasts that their characters have seen. So, if I've got a mountain dwelling druid...they aren't wildshaping into a Killer Whale...at least not until they've seen it. Nor are they Polymorphing into a Killer Whale. They might know they exist but don't have any clue what they look like or how they function. I think a lot of us forget that sometimes. Druid Wildshape is limited to beasts that the character has encountered or seen. That's really important. Sure, it's frustrated some of my druid players who wanted to go right in with a Dinosaur form...but this mechanic does allow the DM a measure of assistance in preparation. What biome was the character from? Right, then any beast with that biome tag here on D&D beyond is fair game...otherwise your character hasn't seen it and isn't able to wildshape into it. The extension of that to Polymorph is of course a houserule but one I think is fair. I might know a Vulture exists in the real world, but I couldn't even begin to describe one, let alone remember what one looks like. 


So play the environment and the encounter set up. Give the players out of combat challenges that lend themselves to the druid needing to wildshape. And remember the limitation...if your character hasn't seen it, you can't use it.

First, thanks to all for the responses. All helpful and give me something to think about.

Aqualain: the scenario you describe is a great one, but I'm pretty sure the player would go pragmatic right away rather than RP and probably just chalk up the lions as losses. The group overall isn't heavy on RP and tends to be more tactical in their gameplaying approach. 

Yes, I do enforce the "You have to actually seen the creature live, in person, to change into it" rules for wild shape and polymorph. They have seen mammoths but there are no dinosaurs in my current campaign world. Some things I allow for extrapolation (giant versions of mundane animals - eagle, elk, etc.) because if you've seen one and the druid presumably knows bigger versions exist, it's not a huge leap to what they look like. Next campaign I might be a bit more rigid on that ruling, though.

But ultimately, yeah, Tier 2+ play is challenging for the DM. I think I'm going to need to start getting more creatures with spellcasting abilities - especially dispel magic and counterspell. My players group is pretty good at shielding the squishier party members, so I think I'll need creatures with challenging combinations of movement, traits, and types of damage, as y'all have suggested.

Quote from Xukuri >>

But ultimately, yeah, Tier 2+ play is challenging for the DM. I think I'm going to need to start getting more creatures with spellcasting abilities - especially dispel magic and counterspell. My players group is pretty good at shielding the squishier party members, so I think I'll need creatures with challenging combinations of movement, traits, and types of damage, as y'all have suggested.

 
I feel you on this. My two campaign groups are both now Tier 2 at either level 7 or 8 and it's around levels 7-12 I find the most challenging. I feel I'm always swinging between too harsh and too easy. So I tend to set up encounters that aren't designed to be solved with combat but have other options for solving or overcoming them. I won't lie I've looked at counterspell, dispel magic and antimagic field recently as a way of offering a real challenge. 

Though I invariably make a rod for my own back sometimes. I give 'interesting' magic items as loot on occasion. Players don't get to request the items or just buy them. They have to find these items or have them commissioned (if they find the right person). So I have players with things like rod of the python, slippers of spider climbing, handy haversacks, javelin of lightening, beads of force etc. Things that don't add huge buffs to AC or attack but do allow the players to think more tactically.

I mean, the logical approach here is to give them more encounters, so that they burn through those wildshapes and are left using other things to fend for themselves. What you're currently seeing is that they are very good at taking a lot of damage in small, powerful encounters. So increase the quantity, not the quality, of the encounters. Where thye may have had 2-3 hard encounters, throw 5 at them, and they'll have 2-3 where they outright can't do much.

Trick them into wildshaping - run a smart enemy who is "ground based", the druid picks the snapping turtle, then watches as they unfurl wings and fly out of reach. The druid then has the choice of being useless for the battle, or un-wildshaping, or wildshaping again.

Something as simple as putting some bandits up some trees could be all it takes. Someone steps out to challenge them, druid turns into something powerful (as is their thing), and then they find out there are some people out of reach, allowing the rest of the party to get involved.

You can expect the druid to be survivable, but a smart enemy will avoid them where possible. You're not aiming for a TPK, after all, but to make the story with the players. So perhaps the druid will always survive, but the squishy wizard isn't getting any benefits from the snapping turtle if the enemy stop shooting it. 

In tier 2, my rule of thumb for even reasonably challenging encounters was 'total party level/2 = total monster CR', with room to go up from there (top end involved some custom monsters who I never bothered to work out CR for).

All you have to do is hit things other than the druid.

Moon druids are in a way a blessing for DMs because you can rebalance encounters on the fly just by attacking the druid more or less.

Wild shapes are usually pretty weak other than when bear is first available. 

There is a low +hit and pretty mediocre damage when they do hit, and tend to have lowish AC.
At that level the turtle only has a +6 to hit, while other martials are going to be at +9 minimum.  With magic weapons that could be a +10 or +11.

The only thing the only big advantage of wildshape at that level is a big pool of hp, which can just be ignored at the DMs discretion.

I ran a barbarian/moon druid in a game and I became the menace of that game. I was nigh unkillable, and I felt my DM was struggling a bit to handle me. To help him get a better understanding of combat balance, I gave a link to the tank fallacy from RPGbot. While they didn't coin the term, its a way to handle "tanks" in DnD that are hard to kill.

You will waste tons of resources trying to kill the moon druid head on. Instead, go around them and attack the rest of the party, especially the squishy ones. This will cause the moon druid to react to this and adjust, giving him a challenge when it comes to decision making. My DM started doing this and I loved the challenge. I no longer could just focus on what I wanted to, I had to make decisions on where I needed to be and who to protect. And if there was a ranged threat that had to be taken care of quickly, I had to either close that gap quickly and leave my teammates behind or literally body block for one character using LOS and abandoning another. 

Mental saves are something moon druids are weak against, especially any CHA or INT saves. WIS saves may be difficult for you to cast on the moon druid because...druid, but if you can get your hands on any powerful int spells (i gracefully failed a feeblemind spell save and had to have the cleric greater resto me) or CHA spells (such as banishment...also, I got banished too and couldn't do a damn thing for almost a minute as my party struggled) then you'll give them a different challenge than just running at things and tanking/hitting.

For a comparison, one of my current characters is an 8th level moon druid. I do use wild shape, but it's rarely going to happen early in a combat, because I'm way more effective in human form and able to cast spells -- my damage isn't huge even then, but pretty much anything higher level than a cantrip is going to be more useful than what I can do in wild shape. Mostly what it's used for in combat is "I'm about to go down, a pile of bonus hp would be useful" and "It looks like time to run away, something with mobility would be good".

Interesting.

I haven't encountered the issues you are having with your moon druid. I have a 1 monk/10 moon druid in a game I am currently running and it is a fun character but really isn't a problem.

None of the level 11 characters in the party are a problem. The most challenging feature I find to balance around is the Monk's stun ability which is pretty awesome. It also makes encounters with a few difficult opponents much more challenging when the creatures make their stun saves and sometimes trivially easy when they fail. Burning through legendary saves can also be greatly facilitated by a monk using stun.

All level 9 characters should feel powerful. A druid has a bag of hit points. A cleric has Banishment and several level 4 and 5 slots to cast it with. Banishment will take a major opponent or two out of the fight for 10 rounds. This spell makes a fight shift very quickly and usually has far more impact than a druid.

One of the best level 9 forms for a druid is the Giant Scorpion ... and that is mediocre. It has three attacks - two of which can grapple, AC15, 52 hit points ... but it only has +4 to hit. At level 9, everyone else in the party is looking at +8 or +9 to hit typically and possibly more with magic items. Killer Whale has one attack at +6 to hit. Basically, the best contribution from wildshapes IS hit points - they make moon druids difficult to take down by whittling away hit points. However, they aren't much of a threat a lot of the time so the opponents may decide to ignore the druid (or they might not). At level 10, moon Druids pick up elemental wild shapes which are much more interesting and very cool and carries them for a few more levels BUT they aren't OP either.

Also, keep in mind that moon druids get their wild shapes back on short rests. This means that they can assume different forms typically 4 to 6 times in an adventuring day assuming at least 1 or 2 short rests.

As the game gets to higher levels, the challenges often shift away a bit from just doing massive amounts of hit point damage. Give the party tactical and strategic goals they need to attain at the same time as the combat encounter. Have the characters deal with spells and opposing spell casters. There is a lot of variety that a DM can use in encounters to provide interest and variety while avoiding every combat turning into a hit point grind.

TL;DR The moon druid isn't OP (except at level 2 ... which doesn't last long :) ). However, as everyone's hit points increase with level, the DM needs to come up with alternative ways for some of the combat rather than just trying to grind away hit points since characters in general have a lot and the entire point of the combat wildshape features IS to provide lots of hit points and durability for the moon druid since the attacks are generally fewer and less effective than everyone else in the party.

 P.S. Polymorph is a separate consideration since druids are only one of several classes that can cast it. Polymorphed creatures attacks are NOT magical. At level 9+, opponents often have a lot of hit points or require magical weapons to do full damage. This reduces the effect of polymorphed characters. In addition, many level 9 characters can out perform the perennially popular T-rex. The T-rex has good hit points, awesome to hit bonus (+10) and decent damage from two attacks but that is all it does. It is also huge which can greatly limit the locations it can fight without being squeezed.

Also, remember to remind the players that most polymorphed creatures aren't intelligent. They don't understand languages or someone gesturing at them, even friends. The character stat block is replaced by the beast one. The polymorphed creature won't attack the party and will attack the opponents but it won't be making tactical decisions like switching targets to the optimal target or moving to cut off the escape of a major opponent. The T-rex doesn't know the difference and the party can't tell it what to do. Just reminding the players of the limitations of polymorphed forms can be sufficient to limit their use to when they really make sense.

Quote from Xukuri >>

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Aqualain: the scenario you describe is a great one, but I'm pretty sure the player would go pragmatic right away rather than RP and probably just chalk up the lions as losses. The group overall isn't heavy on RP and tends to be more tactical in their gameplaying approach.
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 perfect!! what if you'd sent two NPC druid guides to lead your party there? they witness this pragmatism with secret horror. unless someone's quick and lucky with an insight check (but certainly don't force it), they leave quickly soon thereafter. a few days later there's a surprise summons waiting for the druid. they're being called to a druid tribunal. dun dun DUN!

...and this isn't meant to be a way to force the druid to role play 'properly' or bring them into line or whatever. this is purely an opportunity to lean on the existing druid lore that doesn't see enough light in most campaigns. if they bow their head and promise to be good little bears, well, okay. if they stand up and defy to their face the council of elders saying they hide from the world and those who defile it, well, cool! for even more fun, tell the party they can come witness but they have to leave all their metal behind. can they do that safely? will they feel defenseless and hatch a plan to smuggle weapons in? has anyone in the party been on spectacularly poor terms with nature previously or have with them a demon familiar? etc etc.

Others have said how offensively weak a wildshaped druid is compared to other level 9 characters.In fact level 9 is a point where Moon druids are least powerful as at level 10 they can take an elemental form which is much more powerful (though it does use both their wild shapes)

Let me put some numbers to that by comparing to another class that hits, possibly grapples and not a lot else the barbarian, to keep things simple I'll put his ASIs in strength (GWM would be much more powerful) so he has strength 15 and give him a +1 great sword and mundane half plate (very concervative for level 9). I'll put this up against a giant snapping turtle as that is a form you are concerned about (as a rule I don't allow beasts from adventure books as many are broen but this doesn't seem too bad, never allow a druid to wildshape into Onyx)

The giant snapping turtle has 1 attack +6 to hit for 18 average damage. IIf the target has an AC of 17 (average) it has a 50% chance to hit so will do on average 9 points of damage.

The Barbarian assuming he is raging has 2 attacks +10 to hit for d12 +1 + 5 + 3 = 16 damage each hit. He has a 70% change to hit so that totals 22 damage if the barbarian goes reckless it is nearly 30. This is ignoring anything that subclasses or other features give you for example a Zealot barbarian would have this damage increased by around 7 due to divine fury.

The turtle is virtually no threat so enemies will just head to the rest of the party, taking the op attack if needed because they are the ones that can really hurt.

For the druid to keep up damage wise they need ot use their 3rd and 4th level spell slots on summoning spells so the summoned creature adds to their damage. As an alternative they can use those spells for crowd control / support with spells like hypnotic pattern or polymorph (either on a badly wounded allay or to turn the enemy boss into something harmless, while on land my favorite option is a killer whale, it can't move anywhere and has enough hit points to make it hard for his minions get his hit points down to 0) 

Quote from rumloverum >>

Quote from Xukuri >>

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Aqualain: the scenario you describe is a great one, but I'm pretty sure the player would go pragmatic right away rather than RP and probably just chalk up the lions as losses. The group overall isn't heavy on RP and tends to be more tactical in their gameplaying approach.
...

 perfect!! what if you'd sent two NPC druid guides to lead your party there? they witness this pragmatism with secret horror. unless someone's quick and lucky with an insight check (but certainly don't force it), they leave quickly soon thereafter. a few days later there's a surprise summons waiting for the druid. they're being called to a druid tribunal. dun dun DUN!

...and this isn't meant to be a way to force the druid to role play 'properly' or bring them into line or whatever. this is purely an opportunity to lean on the existing druid lore that doesn't see enough light in most campaigns. if they bow their head and promise to be good little bears, well, okay. if they stand up and defy to their face the council of elders saying they hide from the world and those who defile it, well, cool! for even more fun, tell the party they can come witness but they have to leave all their metal behind. can they do that safely? will they feel defenseless and hatch a plan to smuggle weapons in? has anyone in the party been on spectacularly poor terms with nature previously or have with them a demon familiar? etc etc.

This is based on one possible interpretation of a Druid's morals but it is far from the only one and assumes that every Druid could be expected to want to free trapped captured animals whose hides are destined to be made into products. In addition, no matter how you want to frame it, it is an attempt by the DM to coerce the player into playing their druid following a specific code.

Is the PC a member of this particular circle of druids? What gives them any authority at all over the character's actions?

I agree that many folks might consider druids from an animal loving perspective and many would play them that way. However, the lore says that they are interested in nature and balance. Humanoids are as much a part of nature and balance as the animals are. Animals are regularly hunted (in D&D) both by other animals and by humanoids for both food and other resources that are used to make things. Where do you think Druid hide armor comes from? Where does the leather used to make their leather armor come from? Are all druids vegetarians? (Personally, I don't think so).

Below is the lore on druids from the PHB. It describes a wide variety of druids that could have a wide variety of motivations. It would be a completely valid interpretation for a druid to allow the animals to suffer their fate since it is part of the normal cycle of life and death in the D&D world. So having some other circle of druids that is strongly protective of all animals step in and criticize a druid that is a member of a circle for balance or perhaps not a member of any particular circle would be out of place since that circle would have no authority over the actions of the druid. Their very interference could be taken as a sign of their lack of balance and perhaps an indication of unsuitability to be druids.

Finally, just FYI, personally I would usually play a druid as you describe since that is how I would role play my druid but as a DM I wouldn't utilize some sort of in game plot device to force my players to play or even consider playing their druid that way.

Lore:

"Druids revere nature above all, gaining their spells and other magical powers either from the force of nature itself or from a nature deity. Many druids pursue a mystic spirituality of transcendent union with nature rather than devotion to a divine entity, while others serve gods of wild nature, animals, or elemental forces. The ancient druidic traditions are sometimes called the Old Faith, in contrast to the worship of gods in temples and shrines.

Druid spells are oriented toward nature and animals—the power of tooth and claw, of sun and moon, of fire and storm. Druids also gain the ability to take on animal forms, and some druids make a particular study of this practice, even to the point where they prefer animal form to their natural form."

"For druids, nature exists in a precarious balance. The four elements that make up a world—air, earth, fire, and water—must remain in equilibrium. If one element were to gain power over the others, the world could be destroyed, drawn into one of the elemental planes and broken apart into its component elements. Thus, druids oppose cults of Elemental Evil and others who promote one element to the exclusion of others.

Druids are also concerned with the delicate ecological balance that sustains plant and animal life, and the need for civilized folk to live in harmony with nature, not in opposition to it. Druids accept that which is cruel in nature, and they hate that which is unnatural, including aberrations (such as beholders and mind flayers) and undead (such as zombies and vampires). Druids sometimes lead raids against such creatures, especially when the monsters encroach on the druids’ territory.

Druids are often found guarding sacred sites or watching over regions of unspoiled nature. But when a significant danger arises, threatening nature’s balance or the lands they protect, druids take on a more active role in combating the threat, as adventurers."

i did mention that it's not there to force anyone to do anything. this assumes there was no table talk to the player about the consequences of their actions. i just happen to see a story hook in the whole passing up caged beasts angle. ymmv. if your druid wants to get a metal belly button ring and flip the bird to the old guy in the antlers, then that's between that druid and their beliefs. shrug.

if this particular pragmatic moon druid wants to say "i don't know those guys" and ignore the summons, well, it might mean very little. or it might affect the whole campaign. a dm throws out options like a fisherman, switching bait as it suits the weather or not. reeling them back in is a whole 'nother thing. you can stick this in your tacklebox or not as you like. anyway, i didn't mean this to derail more than it did. i'll watch the druid forums for a few days if you want to dig deeper.

Quote from David42 >>

 

Also, remember to remind the players that most polymorphed creatures aren't intelligent. They don't understand languages or someone gesturing at them, even friends. The character stat block is replaced by the beast one. The polymorphed creature won't attack the party and will attack the opponents but it won't be making tactical decisions like switching targets to the optimal target or moving to cut off the escape of a major opponent. The T-rex doesn't know the difference and the party can't tell it what to do. Just reminding the players of the limitations of polymorphed forms can be sufficient to limit their use to when they really make sense.

 
This is a good reminder. I've been allowing players to conflate "personality" with intelligence and shouldn't be doing so.