What's a good method of giving a certain monster resistance to ranged attacks made against it?

Question

I'm creating a monster of my own and I ran into this problem.

So, the monster is a giant, venomous Starfish, largely inspired by the Crown of Thorns starfish in real life. It's about 20-30 feet in diameter, and I gave it a base movement speed of 5 feet per round. I also gave it lots and lots of resistances and immunities to different types of damage, however I'm looking more into the damage source, rather than the damage type.

Currently, it hinders melee attackers by dealing automatic acid damage every time it receives a melee attack (except for polearms). The idea being that you can't really get close to this thing without plunging your arm straight into its spiked back.

It's main method of attack is something I call "Toxic Spear". It only makes one of these attacks per turn, and can make one as a legendary action as well. This starfish creates a valuable liquid metal within its body, and secretes it through small pores in its body, ejecting it at high speeds. This supercools the metal into a long sliver, or a spear. Naturally, this metal is very acidic, and valuable, hence why characters would seek this creature out in the first place. this may be its main (and only) method of directly attacking somebody, but I only gave it 30 feet of range for this attack, which leads me to my problem I'm running into.

My biggest issue that I have with this, is that it would be fairly easy for a ranger, or spellcaster to sit 60 feet away and snipe this thing to death. Obviously I don't want this to happen, because that would be very exploity, and not very fun. So to make it interesting, I wanted to hinder ranged attackers from damaging this beast in some way, but I'm not sure what's a fair ability to give it. I don't want to make ranged attacks completely useless, but I think it makes perfect sense that this hulking, spined being of sheer armor wouldn't be phased, or piercable by arrows, or rocks or whatever you want to throw at it.

Let me know what you guys think, because this beast is generally non-aggressive, but I can imagine players would want to kill it anyways, and I want to give them a hard time for doing so.

Answer 1

There are two really good answers here, but while there's some overlap, they both miss some of eachother's best points IMHO, so I'm going to kinda combine them in my own. I'll leave actual figures out so you can replace them with figures that match the CR you want to build.

Healing

As Pyrotechnical mentioned, starfish are really good at surviving incredible damage, growing back multiple limbs etc. The legendary monster version of this might entail allowing a small automatic start-of-the-turn regeneration ability, as well as a larger healing action or legendary action.

Poison

Actual Crown-of-Thorns Starfish secrete toxins which are really no fun. While acid damage makes sense with the spear you've designed, poison opens up the possibility of residual damage over time, making single long range attacks (and damage dealt due to suffered melee attacks) scarier. Many submarine creatures have paralyzing venom, which could be another way to up the stakes.

Environment

Obviously starfish generally live in the sea - this imposes some pretty hefty difficulties on ranged attackers. It's also worth noting that as water is thicker than air, tremorsense would make sense, and would give an especially good advantage if this creature lives only in very deep water or in submarine caves; Gandalfmeansme details this well in his section about blindsight. I also really like his "Gentle until provoked" idea.

Grappling

Starfish move using lots of suction tubes under their body. This could be part of a melee attack, a possible consequence of the creature being targetted by a melee attack, or connected with a suction legendary action such as the one suggested by Pyrotechnical:

The Crown of Thorns creates a large suction force directly in front of it. All creatures in a 120' line must succeed on a DCXX Strength save or be pulled to within 5' of it and are stunned until the start of the Crown of Thorns' next turn. Succeeding on the save pulls the creature 30'. Anyone concentrating on a spell in the line, must succeed on a DCXX Concentration save or lose concentration.

Perhaps rather than being stunned they are grappled - obviously this nerfs the ability somewhat, as the PC wouldn't lose their actions and attacks against them wouldn't have advantage, but as ranged PCs often don't favour strength it could be a longer lasting effect.

Suggested build:

I've made a couple of slight changes to help the build work, such as increasing the range of the Toxic Spear attack a little to counteract the slow speed, allowing it to hit creatures that have escaped grappling at least one extra time.

• Senses: Tremorsense 120 ft.

• Regeneration: The Crown-of-Thorns regains XX hit points at the start of its turn if it has at least 1 hit point.

• Toxic Thorns: Any creature making a melee attack against the Crown-of-Thorns must make a DC XX Dexterity saving throw or become poisoned. They take XX poison damage, or half as much damage on a successful throw.

Actions

• Acidic Spear: Ranged Weapon Attack, reach 60 ft., one target. Hit: XX piercing damage and XX acid damage. The Crown-of-Thorns ejects a high speed stream of metallic acid which hardens into a long sliver or spear.

• Re-grow: The Crown-of-Thorns focuses it's energy on repairing damage and re-growing lost body parts. It regains XX hit points, and if any of it's arms have been severed, one re-grows.

• Grapple: The Crown-of-Thorns makes a grapple attack with one of it's arms. The maximum number of creatures that can be grappled by the Crown-of-Thorns at any one time is equal to the number of arms it has.

• Paralysis Spear (Recharge 5-6): The Crown-of-Thorns coats it's Acidic spear with a toxic secretion. On a hit the target also takes XX poison damage and must make a DC XX Constitution saving throw or become paralyzed.

Legendary Actions

• Acidic Spear: The Crown-of-Thorns uses Acidic Spear.

• Grapple Attack: The Crown-of-Thorns makes a Grapple Attack with one of it's arms.

• Ensnaring Current (Costs 2 actions): The Crown-of-Thorns creates a strong current pulling towards itself. All creatures in a 120 ft. line must succeed on a DC XX Strength save or is pulled adjacent to the Crown-of-Thorns and becomes grappled. On a successful save the creature is pulled up to 30 ft., but does not become grappled if this brings it adjacent to the Crown-of-Thorns. All creatures pulled adjacent to the Crown-of-Thorns suffer the effects of its Toxic Thorns as though making a melee attack on it.

Bonus Higher CR version

You could also have an Ancient Crown-of-Thorns so you can swap things around and give yourself more range for encounters. Perhaps the Ancient one could have a devour attack where it attempts to swallow a creature that it is currently grappling.

Answer 2

Consider the environment.

Not all the strengths and weaknesses of your monster have to be considered in a vacuum - consider changing the layout of the location it appears in instead.

The main weakness of ranged attacks in a universal sense is being caught in close-quarters where they become vulnerable to melee attackers. Consider placing your monster in an environment where it can harass ranged attackers at close range, and/or where it has minions that can assist it by doing this in it's stead.

Simply put, there is no chance of it being "sniped from 60 feet away" if the room it's in is less than 60 feet big.

Answer 3

The first thing that I think is worth noting is that a lot of ranged weapons are less effective in their attack range when used in water. I strongly recommend you fully familiarize yourself with the underwater combat rules listed on page 198 of the PHB.

The second thing I would consider is expanding the list of options this creature has available to it for legendary actions. You always have the option to give the creature more options for it to use with it's legendary action besides just attacking (which sometimes can be pretty bland). I based some of this upon the real world creature you are trying to mimic and some on what I think makes for a more interesting fight. Since you've a large, slow monster and want to keep it that way, a lot of these focus on letting it control the field by bringing things closer or enhancing survival.

Some potential additional options for that legendary action that would specifically help you would be:

• The Crown of Thorns creates a large suction force directly in front of it. All creatures in a 120' line must succeed on a DCXX Strength save or be pulled to within 5' of it and are stunned until the start of the Crown of Thorns' next turn. Succeeding on the save pulls the creature 30'. Anyone concentrating on a spell in the line, must succeed on a DCXX Concentration save or lose concentration.

This is a nasty option that I think strikes a good balance between punishing excessive use of long-range, while also not letting the creature managing more than 1 or 2 stuns per round. This is long enough to keep those using Eldritch Blast at bay, but not so long that those who've taken feats like Spell Sniper are screwed out of the benefits of that.

• The Crown of Thorns focuses on preserving itself and regenerates 20 hit points.

Straight hit point recovery helps a lot with big monster survival.

• The Crown of Thorns regrows its outer spines to function as an additional barrier and gains 20 temporary hit points.

You might want to pick between either this or the second one, but starfish are really good at living through things that should've killed them.

• The Crown of Thorns throws a spine at an enemy within 120' of it. If the attack hits, the target takes 1d12+Str Mod damage and must succeed on a DCXX Con save or be poisoned for 1 hour. The target may repeat the save at the end of each of its turn.

Looking up the real creature indicates that it is no picnic to get stabbed by those spines. Let's make that a way to really nerf the effectiveness of being too far away.

Answer 4

Restrict visibility, and up the monster's ranged damage

Since you said "resistance to ranged attacks," I thought you might mean damage resistance: you could simply do that, give it "Resistance to damage from sources other than melee attacks." But doing that will still make "kiting" it the best strategy, and practically resource free. Of course, you could just give it immunity to damage from sources other than melee attacks.

But I urge you not to.

Players running ranged characters deserve the chance to run their character any way they choose. So I think you made the right decision to avoid immunity to ranged damage.

I have two main suggestions:

I'd suggest you do the following:

1. Give it blindsight, 120 foot radius
2. Up its ranged damage (to about 1/3 of a single PC's total hit points) per round, and up its ranged distance to 120 feet
3. Have it live deep underwater, so deep that it is in total darkness (perhaps its eyes are very sensitive, and it always retreats from light, regardless of the source).

Darkvision is limited

Many PCs will have darkvision, but few will have it further away than 60 feet (and almost none will have it further than 120 feet). By giving your monster such a large blindsight radius, you ensure that it can see PCs before they can see it.

If a PC tries to kite the enemy from even further away (say, with a longbow from 140 feet), and take disadvantage because they can't see the monstrosity, let them try. Describe the arrow vanishing into the darkness. And say nothing else. Now it's their turn again: what do they do? Now the PCs have to wonder. Did they hit it? Is it coming for them? Is it retreating? If they fire again, will it have moved? Pretty quickly, it will become apparent that this strategy has too many unknowns (if they keep trying it, give them three rounds of silent distant hits, then it's moved 15 feet away and out of range: but they don't know that. They could fire arrows for quite a while into empty water. And if they say "well, I just keep shooting", then after 20 rounds [which you can fast forward through] it suddenly comes into view from the side!).

Ranged attackers will also be restricted by the fact that ranged weapons don't function as well underwater (working only up to "short" range). Of course, a spellcaster could still whip cantrips from a considerable distance, but then they run into the visibility problems I mentioned above.

It gives as good as/better than it gets

Your starfish can return fire at faraway attackers who attempt to "kite" it while it is visible. And if a single character (like the Ranger) tries to do so alone, they will quickly realize the plan will drop them before they drop the monster.

In order to defeat this creature, they'll either need to get creative (perhaps casting dancing lights, or trying to lure it into a trap), or at least ensure that their entire party is doing damage to it at the same time. If you have a mix of ranged and close-range characters, everyone will get a chance to shine.

Gentle until provoked

To make this creature fun to fight, rather than a TPK machine, it is crucial that the starfish is "non-aggressive," like you said. PCs will be able to swim very close to it before attacking if they wish, and start combat with your melee characters up close and your ranged characters far away. The ability to start combat where they want will be essential: most players move at half speed underwater. Giving this creature such a large effective range, while also reducing your players' movement, ensures that if this creature can attack the PCs as they approach, it will decimate them.

If none of this sounds good to you: enjoy being sniped

Your creature design as it stands is interesting, but it absolutely cries out to be kited and sniped. And that's not necessarily a bad thing. There are a lot of ways to make such an encounter interesting. For example, what if while you're kiting the starfish, a much larger one rises from its burrowed hiding spot under the PCs (Mama's angry!). Or have the smell of blood attract sharks, who go after the PCs first. Or the starfish squeezes into a nearby cave, which twists and turns in such a way to stop PCs from hitting it from extreme distances.

But if you insist on having the creature stay in the open, have a slow speed, and a low effective range, then ranged attacks are simply the only reasonable approach for your PCs to take.