"A powered creature is one that has been infested by a powerslug. They appear to be normal members of their species but bulging with exaggerated musculature. They seem hyperactive, jittery, and unusually suspicious."
Aren't you mixing the Description and the Background there?
Actually, would it make sense to give Powered Creatures an SQ where their initial attitude is a step worse than usual or something?
Not sure I'd go as far as making it an actual Special Quality. Maybe mention the possibility in the Description?
Hmm…
The creature bulges with exaggerated musculature and seems unusually agitated, jittering with nervous energy.
A powered creature is a warm-blooded creature that has been infested by a powerslug. They are unusually suspicious and aggressive, so their initial attitude towards beings they encounter is usually at least one step worse than is normal for their species (i.e. if a creature of its kind is normally Indifferent, a powered creature is usually Unfriendly and may be Hostile).
Plus we still need a Background for the
Powerslug itself.
How about:
A powerslug is a very rare parasite found in bogs, tropical swamps and jungles. The slime exuded by the slug is anesthetic: creatures may see or hear a powerslug crawl upon their skin but they will never feel it. Powerslugs can phase themselves away from the Prime Material Plane to become intangible while remaining visible. While useful for avoiding threats this serves a more sinister purpose. Once the slug finds a warm-blooded creature it uses its phasing to enter their body and parasitize them. Powerslugs never share hosts no matter how large they might be; a slug will not enter a creature if their bloodstream tastes of another powerslug's infestation.
Powerslugs feed off adrenaline and similar chemicals. A slug fastens onto its host's adrenal gland and forces it to go into overdrive. The flood of chemicals enhances the host's muscles and nervous system, causing them to become far stronger and more agile than is natural as their muscles swell and their movements grow more energetic. Unfortunately, this increased performance comes with a price. The host becomes increasingly aggressive and violent, eventually fighting to the death at the slightest slight or setback. Even worse, the unnatural development of their body puts such a strain on their cardiac system that most victims of a powerslug suffer fatal heart attacks within a few months of infestation. If the host dies the slug just phases out of the corpse to seek new prey.
Druids despise powerslugs for the devastation that creatures infected by these magical pests do to their environment: an outbreak of powerslugs is usually accompanied by a spate of savage animal attacks. Some brutal individuals or cultures actually seek out powerslug infection for the crude physical power it provides, not caring for the risk of heart attacks and senseless violence.
I thought about adding a paragraph about powerslug reproduction, but there's nothing in the original article about how they do it. My best guess is.
Like many gastropods, powerslugs are hermaphrodites. Unlike most they never mate with each other, but fertilize their own eggs while remaining inside their victim. When the slug senses it is in a warm and humid environment suitable for their development, the eggs are laid in a phased condition to exit the host.
So shall I add the above, despite it being entirely of my invention?