“Brain Cylinder” is an acquired template that can be added to any corporeal living creature that has a brain (referred to hereafter as the base creature).
Challenge Rating: A brain cylinder has limited methods of interacting with the environment and typically has no way to attack or defend itself physically, giving it a CR of 1/4. If a brain cylinder retains spell-like abilities, psychic magic, or other significant methods of attacking and defending itself, its CR is equal to that of the base creature –1.
Type: The creature’s type changes to construct.
Size: The creature’s size is reduced by three size categories (minimum size Diminutive).
Senses: A brain cylinder is blind and deaf unless it has active attachments that grant it vision and hearing. Typically, these attachments only grant vision and hearing equivalent to those of a human, so it loses low-light vision or darkvision. A brain cylinder loses all other senses that depended upon a physical body.
Hit Dice: A brain cylinder drops all racial HD but one and changes that one racial HD to a d8. Creatures with class levels retain their HD. As a construct, a brain cylinder does not have a Constitution score and does not gain bonus hp from this ability, but it does gain bonus hp according to its size if it’s large enough. (Most brain cylinders are Tiny and gain no bonus hp from size as a result.) Saves: A brain cylinder with class levels retains its saving throw modifiers from its class levels. A brain cylinder without class levels has base saves of +0 for all three saving throws as a result of its one racial HD as a construct.
Defensive Abilities: A brain cylinder gains hardness 20 from its armored glass casing. It is immune to cold damage and takes half damage from fire and sonic damage. Any energy damage (except electricity damage) inflicted on a brain cylinder is halved before applying its hardness to determine actual damage. Ranged weapon damage is halved as well, and brain cylinders are immune to nonlethal damage and critical hits.
Weakness(es): A brain cylinder is immobile and is treated as an object. In addition to having a Dexterity of 0 (and thus gaining a –5 penalty to AC), a brain cylinder has an additional –2 penalty to its AC. Furthermore, a creature can take a full-round action to line up an attack against a brain cylinder to automatically hit with a melee weapon or gain a +5 bonus on attack rolls with a ranged weapon.
Speed: A brain cylinder is immobile. It loses all the base creature’s speeds.
Attacks: A brain cylinder has no method of attacking. It loses all the base creature’s natural attacks.
Special Attacks: A brain cylinder loses all special attacks that rely on the base creature’s physical body.
It retains all spell-like abilities possessed by the base creature, as well as all purely mental abilities. If the base creature was capable of casting spells, it retains that ability but cannot cast spells with somatic, material, or focus components. It can only cast spells with verbal components if it has a speech module attached (see Languages, below), and cannot target spells if it has no vision module attached. Without a hearing module, a brain cylinder is deaf and suffers a 20% spell-failure chance. Spell-like abilities function normally when used by a brain cylinder, as they are activated mentally.
Likewise, psychic magic functions normally for a brain cylinder, although the traumatizing distraction of being a detached brain makes emotion components difficult. When casting a psychic magic spell with an emotion component, a brain cylinder must make a concentration check (DC = 15 + spell level) in order to cast the spell successfully.
BAB: A brain cylinder has a base attack bonus of +1 but cannot make attacks on its own. If the base creature had class levels and thus retained its Hit Dice, the brain cylinder’s base attack bonus is the same as that of the base creature.
Ability Score Modifiers: A brain cylinder is treated in many ways as an object as well as a construct. It has no Strength or Constitution score, and its Dexterity is reduced to 0 (thus giving it a –5 penalty on all Dexterity-based checks). The trauma of being transplanted from a body to a cylinder results in a –2 penalty to the base creature’s Wisdom.
Feats: A brain cylinder loses all feats gained as a result of racial Hit Dice save for one feat of its choice. A brain cylinder retains all feats gained as a result of class levels and associated Hit Dice. Note that some feats become useless for a brain cylinder if it no longer qualifies for them.
Skills: A brain cylinder treats all skills as class skills. It retains all skill ranks gained from class levels. The brain cylinder loses all skill ranks gained from its racial Hit Dice, but gains skill points equal to 2 + its Int modifier (minimum 1) if it gained 1 racial Hit Die as a result of applying this template. Although a brain cylinder loses the base creature’s skill ranks, it retains the knowledge it had as that creature and gains an insight bonus to the base creature’s skills equal to the base creature’s skill ranks in that skill.
Languages: A brain cylinder retains all the base creature’s languages, but cannot hear or speak unless the proper attachments are affixed to the cylinder.
Attaching or detaching one of these devices to a brain cylinder is a standard action.
Sandy Petersen’s Cthulhu Mythos, © 2017, Petersen Games; Authors: Sandy Petersen, Arthur Petersen, Ian Starcher.