The ridiculous flail snail probably ought to be categorized as a beast, but Volo’s Guide to Monsters declares it to be an elemental, meaning someone casting conjure elemental in the hope of summoning an earth elemental, xorn or gargoyle may end up stuck with one of these instead. Large, tough and most of all slow, the flail snail is technically a brute, but let’s not kid ourselves: This thing isn’t a predator, it’s prey.
Despite that, the flail snail has no effective means of running away when attacked, so it has to rely on a suite of defense mechanisms, the rudest of which is its Antimagic Shell, which has a chance of bouncing spell attacks back at their casters or refracting them into a multidirectional fusillade of force damage. Antimagic Shell, however, is passive. The one and only decision the flail snail needs to make when attacked is whether to use its Flail Tentacles, its Scintillating Shell or its Shell Defense on any given turn.
Note that flail snails, while brilliant in the visual sense, are far from it in the cognitive sense: with Intelligence 3, they’re not going to be employing advanced combat heuristics. A flail snail’s choice of action is going to boil down to a couple of simple rules that it always follows.
Scintillating Shell is a once-per-combat ability. A flail snail is going to hold off on using it until it can gain the greatest benefit from it—an evaluation that the flail snail isn’t intellectually equipped to make. We need to boil it down to something very basic. Normally, per the Targets in Area of Effect table in chapter 8 of the Dungeon Master’s Guide, an ability with a 30-foot radius ought to target roughly six opponents. But if the flail snail waits to use Scintillating Shell until six opponents are within 30 feet of it, it may end up waiting forever—what if it’s being stalked by just two or three hunters? Let’s simply say that it uses Scintillating Shell when its tentacles and Shell Defense are turning out not to be enough to make its assailants go away—but that, at the very least, it knows not to use Scintillating Shell when there’s no enemy within 30 feet.
Shell Defense, as an action, is one-way: it activates a benefit. To deactivate the benefit requires only a bonus action—and why would it ever deactivate the benefit? Following the principle of always interpreting every fifth-edition rule absolutely literally tells us something counterintuitive in this case: Shell Defense doesn’t prevent the flail snail from attacking. “The flail snail withdraws into its shell” seems like it should prevent it from attacking, but contrast the benefit of Shell Defense, a +4 AC bonus, with the Flail Tentacles trait: “If all its tentacles die, the snail retracts into its shell, gaining total cover” (emphasis mine). A +4 bonus to AC isn’t total cover; it’s not even three-quarters cover. Even after the flail snail retracts, something is still sticking out of that shell—and by deduction, it’s the tentacles.
Flail Tentacle, meanwhile, is a plain vanilla melee weapon attack, no special conditions, no riders.
Therefore, when a flail snail is attacked (No! As commenter Scepstherep notes, the flail snail has tremorsense—it will go to red alert whenever it’s attacked or a Medium or larger creature comes within 60 ft of it, and it won’t come back out until that area is clear of threats), its first action is Shell Defense; it uses its movement to move directly away from its attackers, heedless of opportunity attacks (it’s not clever enough to know that such a thing exists). On its second turn, it Multiattacks, using its Flail Tentacles, against a randomly chosen enemy within 10 feet who’s dealt damage to it. On its third turn, if its foes are still hurting it, it uses Scintillating Shell. On its fourth turn, it goes back to Multiattack, but now it attacks only a stunned opponent with its tentacles. On its fifth turn, it Multiattacks, without any further thought given to target selection, and resumes moving away. It never drops its Shell Defense as long as there’s an opponent either within 60 feet of it or dealing damage to it from farther away.
Next: yagnoloths.
I’m interested in your thoughts on the note in the Multiattack description that all available flail tentacle attacks are made against the same target. I’d just as soon allow our multicolored mollusk friend to smack anyone who happens to be in front of it but I wonder what the design intention behind the single-target specification might be.
I think the design intention is, “When the flail snail fights back, make it hurt as much as possible.”
I think it’s because the snail is essentially attacking with its face. It can’t very well be flip-flopping its tentacles around at an enemy at its front, back, and sides. It’ll rotate to face one thing and smack it.
Interesting way to run them. I like the instinctual motivations of such a creature. It’s peaceful until provoked and even then only goes on the offensive if harmed further.
Add the death shriek and I think I can make my group feel guilty about attacking it. Not to mention, alarms tend to attract all sorts of predators. Maybe the equally absurd owlbear would answer said alarm.
Not just predators—scavengers.
I think we have to assume that Shell Defense is intended to have a drawback, otherwise the flail snail would use it the day it’s born and never stop, and its bonus would be simply included in the snail’s AC. Working from the provided text, the snail “withdraws into its shell.” The wording vaguely suggests that the shell is being treated as an external object that the snail is moving into. Based on this, I’d say that when the snail is inside the shell, it can’t attack or move, though this is open to interpretation due to the stat block’s vagueness.
You’d think that, wouldn’t you? But the unwritten, overarching rule of 5E is, “Read what it says, not what you think it ought to mean.” And the fact that withdrawing provides the flail snail AC +4 when it has tentacles but total cover when it’s out of tentacles certainly seems to imply something.
At the very least, this merits a clarification.
I think, ridiculous as it might seem, you’re absolutely correct here. Compare with the Shell Defense feature of the Tortle race:
Shell Defense. You can withdraw into your shell as an action. Until you emerge, you gain a +4 bonus to AC, and you have advantage on Strength and Constitution saving throws. While in your shell, you are prone, your speed is 0 and can’t increase, you have disadvantage on Dexterity saving throws, you can’t take reactions, and the only action you can take is a bonus action to emerge from your shell.
Which specifically notes being unable to move, or take actions.
It does really feel like something is missing here but you are correct in that other sources will often state their drawback. Might be worth pointing it towards Perkins or Mearls and seeing if this makes it into Sage Advice!
Mearls has gone dark on social media, and Crawford never answers my questions. Maybe Perkins might deign to share an opinion.
we might expect that it has some other, non-combat related things that it can’t do while shell defense is up — i.e., maybe it has to stay out of its shell to eat and poop, which is what it’s doing most of the time, and so doesn’t activate that defense unless it encounters an enemy.
The drawback of Shell Defense is probably just that it’s uncomfortable for the snail, or something else that’s [not stated because it’s not relevant to combat].
I actually made notes about the snail a while ago, and came up with a different interpretation.
While not a full elemental (it feeds and requires rest), it is still of an earth elemental nature, and as you noted in What the Monsters Want, Earth Elementals typically want things static and to be left alone. You also noted they are emotional and temperamental.
When creatures on the ground come within 60ft of the snail (it has tremorsense), it enters its shell and waits for them to back off, wanting to be left to its own devices. If ANYONE comes within 20ft, it triggers Scintillating Shell to stunn them, and begin scrawling over to bludgeon out of anger.
Just my way of running it
I don’t agree about its moving toward them, but you’re absolutely right about the tremorsense!