However you want to inflict this on your games, I hope you like using it. See you tomorrow with another, probably less weird, monster!
This fish-like creature has a flexible stalk atop its body supporting a pair of eyes and a single-jointed appendage ending in a pincer. It sways back and forth in the air as if swimming through it, creating a haunting whistle as it does.
Unpossibulp CR 22
CN Medium aberration
Init +14; Senses blindsight 60 ft., darkvision 60 ft.; Perception +40
AC 20, touch 20, flat-footed 10 (+10 Dex); weirdness armor
hp 450 (36d8+288); regeneration 15 (see variable DR)
Fort +20, Ref +22, Will +23
Defensive Abilities all-around vision, amorphous, overwhelming mind; DR 20/variable; Immune mind-affecting effects, unpredictable immunities; SR 33
Speed fly 60 ft. (perfect)
Melee pincer +29 (4d6+1/19–20 plus grab)
Space 5 ft.; Reach 10 ft.
Special Attacks disorientating whistle, overwhelming mind
Spell-Like Abilities (CL 36th; concentration +40)
At will—dimension door, greater dispel magic, insanity (DC 21)
3/day—mislead (DC 20), quickened greater dispel magic
Str 12, Dex 31, Con 26, Int 14, Wis 17, Cha 19
Base Atk +27; CMB +37 (+41 dirty trick, disarm, and grapple, +39 trip); CMD 48 (50 vs. dirty trick and disarm, can't be tripped)
Feats Agile Maneuvers, Combat Expertise, Dimensional Agility[UC], Dimensional Assault[UC], Dimensional Dervish[UC], Dimensional Maneuvers[UC], Dimensional Savant[UC], Disarming Strike[APG], Greater Dirty Trick[APG], Greater Disarm, Improved Critical (pincer), Improved Dirty Trick[APG], Improved Disarm, Improved Initiative, Improved Trip, Quicken Spell-Like Ability (greater dispel magic), Tripping Strike[APG], Weapon Focus (pincer)
Skills Acrobatics +40, Disable Device +40, Escape Artist +40, Fly +25, Perception +40, Perform (wind instruments) +31, Sleight of Hand +40, Spellcraft +40, Stealth +15
Languages Aklo, Common
Disorientating Whistle (Su) When an unpossibulp flies, air whistles through the holes in its sides. Creatures that can hear the whistling must succeed at a DC 32 Will save or become shaken for 1 round. On a roll of a natural 1, the creature instead becomes confused for 1d4 rounds. This is a mind-affecting effect. The save DC is Charisma-based.
Overwhelming Mind (Ex) An unpossibulp’s alien mind is an unfathomable whirl of strange concepts anathematic to most minds. If a creature makes mental contact with the unpossibulp, it must succeed at a DC 32 Will save or be stunned for 2d4 rounds. On a successful save, the creature is instead staggered for 1d4 rounds. Once a creature is exposed to this unpossibulp’s overwhelming mind, it is immune to this effect from the unpossibulp for 24 hours. This is a mind-affecting effect. The save DC is Charisma-based.
Unpredictable Immunities (Su) At the beginning of each of an unpossibulp’s turns, roll a D8 to determine its energy immunities (1—acid, 2—cold, 3—electricity, 4—fire, 5—sonic, 6—negative energy, 7—roll a d6 twice or select two, 8—immune to all energy types). If the two d6 rolls are identical, the unpossibulp deals the damage it would have otherwise taken to all creatures within 30 feet of it (DC 32 Reflex halves). The save DC is Charisma-based.
Variable DR (Su) Lawful weapons (not +5 weapons, however) always bypass an unpossibulp’s DR. In addition, at the beginning of each of the unpossibulp’s turns, roll a d8 to determine other ways to bypass its DR (1—adamantine, 2—cold iron, 3—silver, 4—wood, 5—nonmagical weapons, 6—ranged weapons, 7—improvised weapons, 8—lawful weapons). On a result of 8, the unpossibulp takes 50% more damage from lawful weapons. Weapons that bypass an unpossibulp's DR also suppress its regeneration.
Weirdness Armor (Su) A random set of attack rolls strike an unpossibulp, rendering its Armor Class moot. A natural 1 on an attack roll always hits the unpossibulp, while a natural 20 always misses. At the beginning of each of the unpossibulp’s turns, roll a d8 to determine which attack rolls hit the unpossibulp (1—even numbers, 2—odd numbers, 3—numbers evenly divisible by 5, 4—prime numbers, 5—numbers evenly divisible by 3, 6—numbers ending in a specific digit [roll a d10 to determine], 7—palindromes, 8—perfect squares). This also applies to rolls to confirm a critical hit.
An unpossibulp is from a remote dimension where the laws of physics don’t always apply uniformly. Occasionally, a hole opens in such a reality, allowing an unpossibulp to escape and wreak havoc. The alien creature has no discernable agenda and attempts to question it about its purpose are met with baffling responses (“consumption of consumption, “egregious giraffes,” and the like). Likewise unknown are actions which provoke the creature. Brandishing weapons might not catch its attention, but it may go on the offensive based on a specific word or phrase. It also quits combat based on unspecifiable criteria, and it may create an opening to its own reality through which it escapes.
An unpossibulp measures 8 feet in length, with its body only taking up half that length. The creature is simultaneously weightless and impossibly dense when it comes to attempts to determine its weight.