[RPG] What makes the Monstrous Crab so dangerous


It was recently mentioned that the Monstrous Crab is generally capable of wiping out even a powerful 3rd level party. It seems to me that, lacking any anti-ranged capability whatsoever, it is trivially dealt with even by incredibly weak characters simply by staying out of melee with it, which itself seems fairly simple for an organized party of level 3 characters. So what makes the crab infamous for character-death-causing?

Best Answer

The crab is said to come out of the waves, grab someone, and drag them back under. It has a reach of 10 ft., a grapple check that just about cannot be beat at that level, and does massive damage. It’s got astonishingly good AC, and just ridiculously high HP, for that level. It’s also faster than almost-all PCs on land, and much faster than most in the water.

Yes, if you see it coming at you across a plain and have significant ranged attacks, you can kill it. I mean, assuming you stay way, way away from it, since anyone in 90 ft. is going to be charged, grappled, and probably killed, all in one round (27 average damage). So if you can stay several hundred feet out (remember, it’s faster than you are, and if it’s running while you’re trying to retreat and attack, it’s closing the gap by 130 ft. per round), kill it with arrows before it closes, fine. But that’s not the environment where you would encounter it. Instead it grabs you off the beach and drags you under, and really, you’re probably going to die to its Constrict damage before you get a chance to drown.

Also, just compare it to other things at its CR. An ogre is CR 3; it’s got well less than half That Damn Crab’s HP, dramatically lower AC, is significantly less accurate, and the damage isn’t even close (Improved Grab + Constrict effectively doubles each claw’s damage). A giant stag beetle is CR 4 and is damn close to That Damn Crab without any of the extra special features.

When I wrote the above, I gave a party the benefit of the doubt and figured, yes, they probably could kill it with arrows. But its numbers are just so insane, that I decided to actually hash out what that fight looks like. TL;DR: the party should avoid a TPK, but at least one death is basically guaranteed, and losing half the party is likely.

Here’s something like a “typical” fight against That Damn Crab on the hypothetical bare plain. I’ve simplified things dramatically, and a party could probably do somewhat better than this, but at the same time I’ve been generous on a number of points.

  • Four-member party.

  • Entire party has composite longbows, and proficiency with them. BAB +3, +2 from Dex, +1 from masterwork, is a pretty generous +6 attack bonus. 1d8+2, say, for having high Strength. Hit on a roll of 13, 40% chance, average damage on hit of 6.5, 2% chance of a critical hit for average damage of 19.5, expected damage of 2.86.

    • One party member has Str and Dex 18, so +4 from Dex, so +8 attack bonus, 1d8+4 damage. 50% chance to hit, average damage of 8.5, 2.5% chance of critical hit for average damage 25.5, expected damage of 4.675.

    • One party member (an elf conjurer) instead can cast acid arrow three times; 2d4 damage initially (5 average), 4d4 on subsequent rounds (10 average) (we assume that the damage tick happens before the wizard re-applies the spell, so stacking isn’t a concern). Only +3 to attack, but vs. touch AC 11, so 65% chance to hit. Chance of a critical hit, 3.25%, to add another 5 average damage to the initial hit). Expected damage is 3.4125 the first round, 6.6625 thereafter. Notably, 520-ft. range.

      • It’s worth noting that there are much better spells that can change things here dramatically. Glitterdust has a 75% chance to blind the crab for three rounds, which effectively neuters it for that time. Grease or web could slow it down. I went with straight damage for ease of simulation and to make using averages more valid (there’s no such thing as 75% blind the way there is 65% of 5 damage), and frankly the fact that the best 2nd-level spell in the game (glitterdust), which literally could not be more perfect a counter for this crab (abysmal Will save, mind-affecting immunity that doesn’t apply, and nearly zero combat ability while blind), only means you probably won’t lose a party member to this thing, is a pretty strong statement in itself.
    • Archers take −2 penalty for every hundred feet, modifying the expected damage as follows: 0.3575 damage at 400+ ft., 0.715 damage at [300,400) ft., 1.43 damage at [200,300) ft., and 2.145 damage at [100,200) ft.

    • The superior archer gets 0.4675 damage at 500+ ft., 0.935 damage at [400,500) ft., 1.87 damage at [300,400) ft., 2.805 damage at [200,300) ft., and 3.74 damage at [100,200) ft.

  • No one is wearing armor that will slow them down.

  • One party member can actually survive a hit from the crab. They can’t do anything in the grapple (and trying could get them killed), but it forces the crab to waste a turn finishing him off.

  • Surprise the crab from 520 ft., the limit of acid splash. Assume the party goes first after surprise round, too. I won’t let them circle around the crab at that distance and run in opposite directions, however.

Surprise round: wizard, two regular archers, superior archer all attack. At that range, the arrows are fairly unlikely to do anything, but flat-footed their expected damages are 0.3575 (regular archers) and 0.935 (superior archer), for a total of 1.65 expected damage. The wizard, of course, gets 3.4125 damage. Total expected damage: 5.0125.

From there, rounds:

  1. Party attacks again, crab is still flat-footed, so it’s the same damage except the wizard’s damage goes up from the CL 3rd acid arrow’s lingering damage. Expected damage 8.3125 this round, crab should be down to 52.675 HP. They all take move actions to go 30 ft. directly away from the crab.

    The crab runs towards them, covering 160 ft. The gap between the crab and party is down to 390 ft.

  2. Party attacks again, better attack bonuses for the archers now. Party should deal 9.92 damage; crab is down to 42.755 HP. The wizard, however, is out of acid arrow. They move back 30 ft; the wizard pulls out his own longbow (elf, I suppose).

    Crab runs at them again, again closing the gap by 130 ft. The gap is down to 260 ft.

  3. Rinse, repeat. Party damage is down to 7.095 without acid arrow; crab goes down to 35.66. They scoot back.

    Crab closes, shaves another 130 ft. off. Down to just 130 ft. Crab will be among them next turn.

  4. If the party is particularly set on this, they can attack again. Honestly, they can’t outrun it, so they might as well. Damage is up to 10.175, so the crab is down to 25.485 HP. They move back; relevantly, between turns this puts them at 160 ft., so the crab must run.

    The crab does so. At this point, it is adjacent to at least one party member; that person cannot get out of its reach without provoking.

  5. We’ll assume the party is spread enough, at this point, that the crab cannot threaten more than one person. We’ll assume that person has a melee weapon they can use, for the same damage as the longbow. So the party attacks for 13.255 damage. Everyone except the one threatened move back.

    The crab attacks the one who attacked it in melee. Since it can full-attack, that person is dead no matter who they are. We’ll assume the wizard, since he’s done the most damage even if he is out of acid arrow.

  6. Without the wizard, the party damage is down to 10.395. That’s bad, because the crab is still at 1.835 HP. They move back, but...

    The crab charges someone. Probably the superior archer, as the second-highest source of pain to the crab. Problem with that is, the superior archer isn’t likely to be the guy who can take this hit. So he’s dead.

  7. The remaining half of the party get to shoot at the crab; their 5.72 damage is enough to drive the crab into negatives. This leaves it dying, and they can finish it off at their leisure.

Result: crab dies, but takes two party members with him. A CR-3 threat is defined as one that takes appropximately 20% of a party’s daily resources to kill. It is not supposed to wipe out half the party under conditions very favorable to the party.

Related Topic