Similar to Angolmois Energy, the substance Unicron uses to power himself, Amalgomous Energy is almost as poisonous as that dark substance, primarily because it is lacking in certain ingredients such as higher dimensional energy.
The foul substance does not appear naturally in nature and has to be created, often by a somewhat mystical procedure or ritual. The energy is like a drug, poisonous to any form of life but also a mutagen capable of turning creatures into dark parodies of themselves or animating the dead, (only if they are a robotic life form). Amalgomous Energy is poisonous but any life form that can learn to survive on it, is nothing short of a monster. Even when converted into plasma (which can be done easily), it does not loose its poisonous nature. The exact makeup of the substance is known to few being in the universe, in fact the only beings who use it are best described as 'Lovecraftian' in nature.
It is an Eldritch form of Engen, created through unconventional means.
Amalgomous resembles a dark green slime, or energy in its natural state. When weaponized it has a poisonous green glow.