Shadow Fiends

Shadow Fiends, also known as Shadow Demons, are a species from an unnamed planet shrouded in darkness.

Appearance
Shadow Fiends appear as dark purple shadows with bright yellow eyes. Their appearance differs between individuals but in light they are typically a maximum of 3 feet tall and paper thin.

The less light there is the larger and more vicious they become in both appearance and personality.

It is unknown what they look like in complete darkness.

Behavior
Shadow Fiends in their native habitat, a planet shrouded in complete darkness, they are incredibly dangerous creatures. They are potentially 50+ feet tall and completely feral. They have no capacity for reasoning and will violently maul any living thing they find including their own kind.

When exposed to light, Shadow Fiends shrink down(relative to how much light is on them) and become rational and capable of learning.

History
It is unknown how long they have existed as their entire history, if they ever had any, has been lost due to the extensive time spent feral in the darkness. Other races first discovered the planet and due to the lights of the ships, inadvertently calmed the Shadow Fiends. After the discovery that they go feral in darkness, a series of lights was made on the planet keeping it just light enough that they no longer risk becoming feral.

Since the addition of the lights they have began to form a culture and society, with the assistance of other races. Due to having time to learn and become use to their non-feral nature some have learned to control themselves even in complete darkness and a few have joined planetary/universal teams to help protect other planets or solar systems.

Powers and Abilities
Shadow Fiends have the ability to become larger and stronger in direct relation to how little light they are in. When under a decent amount of light, they have the ability to travel in shadows.
 * When fully under light, they are weaker than a human and paper thin although, despite being so thin, they are still incredibly durable and cannot tear.
 * When under just enough light that the human eye can barely see in, they are about the size of an adult man or larger and are much stronger than the average human.
 * When in complete darkness, their size has no known minimum or maximum although 50+ feet is generally accepted. They become practically invulnerable and extremely powerful.

Weaknesses
While light will not kill them, it will severely weaken them.