
Ben Ehrets |

"CLASHING ROCKS (Ex)
A plankta can scatter its rocky mass into multiple fragments with a shared consciousness and a shared pool of hit points, though it loses its stony cover ability when it does so.
These fragments churn and clash, dealing 4d6+14 points of bludgeoning damage per round to all creatures in a 60-foot-radius sphere in the water (extending up to 10 feet above the water’s surface). Activating or maintaining this ability is a full-round action. If it chooses not to maintain this ability, the plankta’s body reforms automatically at any point in the area. The save DC is Strength-based."
A SAVE DC IS MENTIONED, BUT THERE'S NO DISCUSSION OF WHAT THE SAVING THROW WOULD ACHIEVE. Or what kind of saving throw it would be. Reflex?
There is a 9th level druid spell called Clashing Rocks which includes
"If the target fails a Reflex Saving Throw, it is also buried under the resulting rubble as if by a cave-in.
If the clashing rocks miss the target, the target still takes 10d6 points of bludgeoning damage from falling rocks and is knocked prone. A successful Reflex save reduces this damage to half and the target remains standing."
Whatever the save is for, being Strength-based DC means a lot of characters are going to fail this saving throw. If it includes being knocked prone every round, yikes!
I'M ALSO NOT SURE HOW CHARACTERS WOULD ATTACK THE FRAGMENTS. How many fragments? Are we assuming characters could just swing anywhere in the area of effect and hit a chunk to inflict damage on the whole?
Thanks in advance for any advice.

Azothath |
Plankta CR17 NE Colossal aberration (aquatic, earth). These massive, rocky aberrations dwell in the seas... so underwater adventures or naval battles... so check the underwater modifiers and conditions...
Clashing Rocks - it's just extra info so a GM can (hopefully) figure out a DC if needed. See Improved Cover for the AC adjustment. No Stony Cover means it takes damage from anyone in the AoE that can hit its reduced AC.
Stony Cover - there's no mention of Hardness or Hit Points of the cover, Stone = Hrd:8 HPs:90/ft, so it just glosses over those details meaning they're not important. Note that a crit causes a gout of magma (and you can't crit stone as an object/cover).
The creature uses a lot of handwaving and creative writing. Separate the crunch from the fluff.

Ben Ehrets |

Thanks for the thoughts.
I think I get most of it.
I believe "Does plankta Stoney Clash do any of the extra effects of the spell Stoney Clash" is answered with a simple "no". (I only entertained that possibility looking for what the saving throw might be about).
THE CRUX OF MY STONEY CLASH UNCERTAINTY IS "The save DC is Strength-based" WHEN THERE IS NO DISCUSSION OF A SAVING THROW.
The confusion clears if indeed there simply is no saving throw.

bbangerter |

Whatever the save is for, being Strength-based DC means a lot of characters are going to fail this saving throw. If it includes being knocked prone every round, yikes!
Side note:
A Strength based DC does not mean that characters making a save use their strength bonus on the saving throw. It means the DC to beat is based on the activating characters strength.Eg, a typical sorcerers spells are Charisma based DC's, because charisma is their casting stat. Characters saving against those spells still use fort/ref/will as appropriate.
Many creatures with SLAs or Su abilties have Charisma based DCs.
For example
Ghoul Fever: Bite—injury; save Fort DC 13; onset 1 day; frequency 1/day; effect 1d3 Con and 1d3 Dex damage; cure 2 consecutive saves. The save DC is Charisma-based.
So if a ghoul increases or decreases in charisma, the DC needed to save against the disease goes up or down.
Some creatures have abilties based on dex, str, etc.

Azothath |
by design 4 PCs at 14th level can succeed against a CR 17 (APL+3). As it is underwater that depends as the plankta is not hindered by the environment. One hopes the PCs make a know(dngn) 32 (at CR+15) check and discover some weaknesses {BTW sonic & acid spells not hindered underwater and it's Touch AC is pitiful}. At 14th level the PCs can certainly Fly and the plankta's reach with Clashing Rocks is only 10ft above the water.
With Fly and Swim the prone condition has little meaning.
Essentially a big damaging AoE critter but without Stony Cover AC 28(=36-8) in 60ft rad!, TchAC 3, Rflx +9 (=13-4), HPs 313... it'll go down fast. A wizard on a ship with Spectral Hand will drive the plankta off. Consider that most ships have a cannon or two so really they're just facing DR 15/- & 313 HPs critter with a move of 30.

Ben Ehrets |

There's seven reasons our scenario was more deadly than what you describe, but I'm not trying to cancel this monster as overpowered; I was just trying to make sure I'm reading Clashing Rocks correctly, most particularly in regard to it having no saving throw.
I was hoping someone would say directly: "Correct, there is no saving throw."
A nifty bonus would have been someone commenting, "You're right, it is mildly confusing that they mention a saving throw DC when there is no saving throw."
But I am satisfied now with my understanding of the ability and the creature, and I am grateful for all of the comments. Thank you!

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You're not wrong. The ability should either be (no save) or should have a listed save type such as (Reflex half).
After reading the ability several times — If I was the GM I would change this to (Reflex DC31 half) and "the save is Constitution based."
This is based on exactly what the ability does. It's very similar to the Fiery Fault and Rain of Boulders. And according to Bestiary page 292:
Most special abilities that cause damage, such as breath weapons, give a save (Fortitude, Reflex, or Will depending on the ability). The DC for almost all special abilities is equal to 10 + 1/2 the creature's Hit Dice + a relevant ability modifier (usually Constitution or Charisma depending on the ability). Special abilities that add to melee and ranged attacks generally do not allow a save, as they rely on the attacks hitting to be useful.
Not saying everyone must do what I say, etc. Just that's how I would do it.

Azothath |
You're not wrong. The ability should either be (no save) or should have a listed save type such as (Reflex half).
After reading the ability several times — If I was the GM I would change this to (Reflex DC31 half) and "the save is Constitution based."
...
Advice wise you're right (I don't offer advice at first as this is the Rules forum). I think some Home Game GMs would correct Clashing Rocks adding a save and you couldn't blame them. Again, the write-up is very handwaived and creative rather than rule explicit. Being exposed while doing your AoE damage is a bit counter-elemental and the background reads like an undead but it's an aberration...