this ghoulish space-thing infests areas with its gruesome gangrenades and pestilence-projector. The Terror former is actually the weapons and ammunition themselves, they get wielded by some hapless space-adventurer who has come in contact with terror-spores.
Once the spores get into the neural pathways of the victim they start giving him/her the brilliant idea to manufacture these terrible weapons and start using them on everything right away.
After a substantial amount of the terror-mold has networked in an area they start manifesting planetary assault cysts that explode with such force they send their payload through the stratosphere. Each spore has the blueprints of the weaponry and is ready to influence another poor bastard.
It's terrifying but it's oddly compelling to watch! Looks to be that way with The Last of Us, yea. Looks to be a pretty sweet idea for it, too. Some of those trailers are astounding!
I love it!