Now, Shoggoth can be a pain to fight if you're unprepared.
But if the character's are optimized and chew through them pretty quickly it can be a bit boring. So I was thinking of making a unique one for a capstone villain.
Advanced Giant Shoggoth
CN Gargantuan ooze (aquatic, unique)
Init +13; Senses all-around vision, blindsight 60ft, darkvision 120 ft., low-light vision, scent, tremorsense 60 ft.; Perception +35
AC 37, touch 13, flat-footed 30 (+7 Dex, +24 natural, –4 size)
hp 405 (23d8+322); fast healing 10
Fort +23, Ref +16, Will +17
DR 15/—; Immune blindness, charm effects, cold, deafness, ooze traits, sonic; Resist acid 30, electricity 30, fire 30; SR 35
Speed 50 ft., climb 30 ft., swim 50 ft.
Melee 4 slams +36 (3d8+21/19–20 plus grab)
Space 20 ft.; Reach 35 ft.
Special Attacks constrict (3d8+21), maddening cacophony, engulf (4d8+31 bludgeoning damage plus 8d6 acid damage, AC 25, hp 37), trample (4d10+21, DC 38)
Spell-like Abilities (Divine) (CL 20th, Concentration +28)
At-will — quickened dimension door, widened black tentacles
3/day — tsunami, whirlwind
Str 52, Dex 28, Con 39, Int 9, Wis 26, Cha 17
Base Atk +17; CMB +42 (+47 grapple); CMD 61 (cannot be tripped)
Feats Blind-Fight, Improved Blind-Fight, Combat Reflexes, Critical Focus, Great Fortitude, Dimensional Agility, Improved Critical (slam), Improved Initiative, Improved Sunder, Iron Will, Power Attack, Staggering Critical
Skills Climb +29, Perception +35, Swim +29; Racial Modifiers +4 Perception
All-Around Vision (Ex)
A shoggoth's many sense organs grant a +4 racial bonus on Perception and immunity to flanking.
Maddening Cacophony (Su)
As a free action, a shoggoth can give voice to sounds and words sane life was not meant to hear. All creatures in a 60-foot radius must make a DC 24 Will save or be confused for 1d6 rounds. Each round a creature is affected it takes 1d6 points of Wisdom damage. A creature that saves cannot be affected by this shoggoth's maddening cacophony for 24 hours. This is a sonic mind-affecting effect. The save DC is Charisma-based.
To use this ability, the shoggoth must begin its turn grappling a creature or must trample. A shoggoth may attempt to engulf as many creatures as it grapples or tramples in a round. This ability otherwise functions as swallow whole, save that a creature that cuts is way out of a shoggoth leaves no hole in the protoplasmic creature's body.
There are a few things different with this one, such as the addition of SLAs and a few changes to feat selection. There have also been additions in the form of templates, the advanced and giant template. I was not sure how items and oozes interact, so it didn't receive any.
While robust, I still think it could be a challenge to a party of 18th - 20th level characters. Though the additional enemies may be necessary for the capstone fight, maybe advanced black puddings, advanced gibbering mouthers, or other shoggoth.
Would this be too much for an average optimized party of 4 by itself (think classic party; cleric, wizard, fighter, rogue or divine, arcane, barbarian, slayer)?
I was thinking of making the location be like Blackreach from Skyrim.. I think this link will help. (link is an screenshot from imigur and not my own).
If you've ever read "At the Mountains of Madness", remember too that the Shoggoths were able to shape limbs and sensing organs at will or under hypnotic suggestion, and were essentially built as living, tool-using construction equipment by a godlike alien species that the Shoggoths successfully rebelled against and (to a shakier degree) imitated in writing, art, speech, culture, etc.
[The Shoggoths] had always been controlled through the hypnotic suggestions of the Old Ones, and had modeled their tough plasticity into various useful temporary limbs and organs; but now their self-modeling powers were sometimes exercised independently, and in various imitative forms implanted by past suggestion. They had, it seems, developed a semistable brain whose separate and occasionally stubborn volition echoed the will of the Old Ones without always obeying it.... They had... a constantly shifting shape and volume - throwing out temporary developments or forming apparent organs of sight, hearing, and speech in imitation of their masters, either spontaneously or according to suggestion.
You're dealing with intelligent creatures that can ooze their way through tiny spaces that adventurers can't get to, command the strength, constitution and dexterity to lift gigantic stones into place to build vast cyclopean cities, shape the limbs needed to walk or run or swim or fly, form the organs needed to imitate speech, form the organs necessary to employ all the five senses available by default to PCs plus any of a variety of alien sixth senses, imitate other creatures or objects, communicate and collaborate with other Lovecraftian henchmonsters and team members, build and use tools and weapons, mastermind BBEG plots, learn to use magic or gain levels in PC Classes, and much much more.
With all that in mind, consider the titular monster from John Carpenter's "The Thing", and everything The Thing could do to make the protagonists' lives "interesting" (and by "interesting", I mean "a stark, screaming, paranoiac nightmare") - a Shoggoth could conceivably do any of that, and more.
Really, there's no reason that a Shoggoth couldn't be the most interesting (and terrifying) monster the PCs have ever fought....
An unprepared party will get chewed up and spat out before they could blink...
That said, this is a capstone end game boss? So the party will be well aware of what a Shoggoth can do. So freedom of movement/flight and some mind protection will be on before battle begins.
I would also assume the regular tactics of that beast would be blink in, grab (and hurt) as much of the party it can, next round, grab (and hurt) anyone it missed last round, then blink into the deep water, hoping to drown the party, as it is unlikely to ever kill something with slams. Of course, slam grabs for anyone who escaped and blinking deeper with those it can hold onto.
It would definatly be an issue for anyone who might get grabbed and swallowed, so spell caster is gonna be upset. Rogue is not gonna like the lack of organs to sneak attack. Cleric and Fighter might be ok, staying with mostly buff spells and beating the hell out of it. Wizard could do that too tbh, but depends on how he was built, a blaster will end up in the corner crying but a buffer/supporter would be able to contribute. I can see a conjurer being the best at dealing with fuzzy up there, what with minions and buffs to hand out to them. Minions who will eat AoO, or distract slams (occupy some of the stomach so party members do not get eaten).