Not quite a Halloween-themed tidbit, but it was created by a deity-level Mad Scientist character of mine using a variation of the Craft Wondrous Creature feat from the Netbook of Feats (a variation that isn't quite so overpowered or limited in creature types) and the v5 CR rating document to set it's CR and LA.
He created a dozen of them and gave one to a mad scientist friend (who is immune to their charms) as a Halloween gift. Being a god of chaos (amongst other things), he let the rest roam freely in the swamp he lives in, in the hope that they'll breed and become a pest species and unbalance the ecosystem.
He also hopes that people find them, adopt some of them, and end up forgetting all about their responsibilities. In this way, he hopes, they'll contribute to the decay of society. Much like cell phones, entertainers, and the Internet have, by providing a distraction from reality that becomes an addiction/obsession.
Nibblet
Fine Animal
Hit Dice: 1/8d8+5 (6 hp)
Initiative: +5 (+5 Dexterity)
Speed: 40 ft., burrow 20 ft., climb 40 ft., swim 40 ft.
Armor Class: 15 (+5 Dexterity)
Base Attack/Grapple: +0/-21
Attack: Bite +5 melee (1d4-5)
Full Attack: Bite +5 melee (1d4-5)
Space/Reach: 6 in./4 in.
Special Attacks: Adorable as f#@%
Special Qualities: Blindsight 30 ft., lowlight vision, scent, tremorsense 60 ft.
Saves: Fort +7, Ref +7, Will +5
Abilities: Str 1, Dex 20, Con 20, Int 20, Wis 20, Cha 20
Skills: Balance +20, Climb +20, Jump +20, Listen +20, Spot +20, Swim +20
Feat: Beauteous Visage (B), Weapon Finesse
Environment: Any.
Organization: Solitary
Challenge Rating: 4
Treasure: Standard
Alignment: Neutral
Advancement: By class.
Level Adjustment: +6
Nibblets are 6 in. long, whiskered, fluffy, prehensile-tailed mammals.
Nibblets speak Nibblet and whatever language their “owner” speaks.
Combat
Nibblets avoid combat, preferring to look adorable and snuggle.
Adorable As F#@% (Ex): A nibblet is so adorable it continuously replicates mass suggestion (Caster Level 20th). The save DC is Charisma-based.
Skills: A nibblet has a +8 racial bonus on Balance, Climb, Jump, Listen, and Spot checks. A nibblet can always choose to take 10 on a Climb check, even if rushed or threatened. A nibblet has a +8 racial bonus on any Swim check to perform some special action or avoid a hazard. It can always choose to take 10 on a Swim check, even if distracted or endangered. It can use the run action while swimming, provided it swims in a straight line. Nibblets use either their Strength modifier or Dexterity modifier for Climb, Jump, and Swim checks, whichever is higher.
The Create Wondrous Creature variant I used...
Create Creature [Item Creation]
You can create corporeal, living, non-divine creatures.
Prerequisite: Caster (or Manifester) level 5th.
Benefit: If you have an alchemist's lab (v3.5 P.H.) and artisan's tools (v3.5 P.H.), you can create any corporeal, living (non-construct, non-undead, non-undying), non-divine (no quintessence) creature whose prerequisites you meet (see below). However, the creature is not necessarily under your control. To create a creature, you subject a similar creature to experimentation and spells (or powers) and must succeed on both a Knowledge (arcana) (or (psionics)) check and Knowledge (nature) check (DC 20 + CR of the creature). If one Knowledge check fails, the creature is horribly deformed and hostile. If both Knowledge checks fail, the creature dies a horrible death. Regardless of failure or success, you gain a +1 circumstance bonus on subsequent attempts per previous attempt (+20 maximum) to create a specific creature. Creating a creature takes one day for each 1,000 gp in it's price. To create a creature, you must spend 1/25 of it's base price in XP and use up raw materials costing half of it's base price. The base price of a creature is the creature's (CR x 5) squared x 1,000 gp ((CR x 5) x (CR x 5) x 1,000 gp). The minimum caster (or manifester) level for creating a fertile creature is the creature's CR x 15. The minimum caster (or manifester) level for creating a sterile creature is the creature's CR. The appropriate spells (or powers) must be used to add extraordinary (Ex), spell-like (Sp) (or psi-like (Ps)), and supernatural (Su) abilities to the creature.
Special: If charm monster (or charm, psionic w/augments 1 or 2, as appropriate) is cast (or manifested) every day of the creation process, a successfully created creature will be entirely loyal to you, although not under your direct control. If limited wish (or bend reality) is used in the creation process, a successfully created creature will be loyal and will follow a life goal you choose for it. If wish (or reality revision) is used in the creation process, a successfully created creature and all it's descendants will follow a single life goal of your choice.
The 'Beauteous Visage' feat is from Testament. It basically makes it so any reaction to them is 2 categories better (if the NPC isn't already hostile) and it makes it so they can't worsen a reaction via social interaction. They can only improve a reaction.