I’m looking to see if anyone has any good ideas for a big, giant space threat creature. Something comparable to a Crystalline Entity or Fargate Jellyfish alien. (I want to break away from constant call-backs to various episodes for an adventure).
Has anyone conceived of a good threat monster that’s nicely different than ones we’ve seen before?
BC
An episode of my campaign was set in an alternate future where people lived on the inside of a Dyson Sphere. They only existed as a feeding ground for a number of crystalline entities.
Star Trek Armada introduced Species 9341. They were unsuitable for assimilation, that’s way they were eradicated by the Borg. But they could be potentially valuable if one could discover a defense against assimilation.
The Star Trek: Titan novel “Orion’s Hounds” features several cosmozoans, including the Jellyfish species which is used by other aliens as spaceships.
I thought about a cosmozoan which lies dormant in space until a planet has formed around it. Then it feeds on the life on its planet somehow, killing thousands of people each day. I thought this would be an interesting dilemma for a crew.
In one of Iain Banks’ Culture novels, there are Coty-sized creatures called Behemothaurs, which have entire ecosystems inside them.
Something like that might be interesting.
One of the earliest Star Trek adventures I gamemastered a quarter of a century ago was about a gigantic could creature consisting of complexe organic molecules on lead basis which was destroying colonies on both sides of the neutral zone in early 2270s (TMP era). The crew of the completely overhauled USS Reliant had to find a way to stop this creature before it destroys more colonies. They did this by constructing a special torpedo.
What about a creature that feeds on stars, e.g. entering an orbit, collecting solar radiation and emitting some radiation that is dangerous / deadly to humans as product of their digestion? Or maybe something involving subspace? Living in/feeding from/manipulating…
Or maybe a lifeform that manipulates spacetime while moving? 
Never forget the cyclopean possibilites posed by entities f4om Outside, where the angles are all wrong and and the shifting eyes are mouths and you are unsure if it even has a shape, tantalizing some with the lure of lore wont to drive seemingly sane beings mad. The province of Lovecraft and Hermaeus Mora, the deadlights of Stephen King.
flying spaghetti monster
anything that resembles a tyranid (from warhammer 40k) ship
a sentient quasar that moves through different systems and gas clouds to get more mass to feed it
some kind of 'space trapdoor spider" that sucks its prey into a dimensional pocket.
space dragon
space amoeba
a “space worm” that travels via “worm holes”
You know that a quasar is the center of a galaxy and thus a supermassive black hole!
AND it’s super hungry! Stars of the galaxy – beware! 
wouldn’t be the first time that something from another galaxy was invading and needed to be stopped. Okay but maybe a pulsar star, or something else.
An entire supermassive star moving through a system would be enough to destroy everything just with the gravitational pull. Wouldn’t even have to be supermassive… just a regular star, or even an average planet in the right place would totally disrupt a star system.
I mean, a system is built around one or more stars… and now you have another, and it’s moving… and that actually would be a way for it to feed. It tears apart other stars and planets with it’s gravity, absorbing them and becoming larger.
If you want to have a star in your series, try using an avatar like Trance Gemini.
It wouldn’t “destroy” most objects - star systems and planets are much bigger than you might suppose - but it would disrupt orbits. The process would happen very slowly (over months, years or even decades) but depending on the speed, trajectory and size of the invading object, the system would be completely reconfigured.
Deleted a couple of posts there folks.
Please play nicely…
Mod hat off.
Sol is an average star as the Universe goes, but Earth could crash into it and not be noticed.
A supermassive object like a quasar would completely disrupt a system as it moved thru it, and the ewnergy given off would likely sterilize any planets therein, and if it got close enough to the primary would start drawing it into itself.
It might take a while for the effect to be noticed, but not for it to happen.
Yeah a quasar (as in the system of superhot gas and matter surrounding the central black hole of a galaxy) would wreak that kind of damage. You were specifically discussing stars, which are signifcantly smaller.
A quasar or something on the scale of Eta Cassiopiae would definitely wipe out the system - some time before it actually arrived there!
I was referring to the quasar or pulsar originally suggested by JDW, and suggesting even an ordinary star would destroy any system in travelled thru.
Sorry if it wasn’t clear
Even an object of the size of a small planet or a moon would wreak havok with any solar system it passes.
V’ger in its large size of several AU could not have an equaly huge mass, because it would have the same effect on a solar system as a black hole. Thus the V’ger could could not have a significant mass and V’ger itself could not be larger that a large space station.
A quasar would definitely wipe out the whole system, a pulsar would incinerate anything caught by the beams, and both a pulsar and a star would disrupt orbits which would likely destroy the system - but not the worlds. (Except in the long run of course.)
Note that the chances of an actual collision with a body in the system are very small.
They’re all very different things - even if Trek’s writers never really figured out the difference!
Sorry, but no, it wouldn’t. You’d need something significantly more massive to “wreak havok” - a body the size of Neptune would distort orbits as it passed through and leave some worlds on very different paths, but it would leave most of the system untouched. A moon-sized world would sail merrily through, be deflected from its original path by the star’s gravity and then leave again. It would affect very little.
I believe V’Ger the vessel was less than a hundred km long, making it the size of a small dwarf planet. It probably had a high density and therefore an higher mass. The cloud’s mass would have been less. Again not much in the grand scheme of a star system.
Sorry, but every mass influences everything around it. your moon-sized world would not “sail through” a solar system and leave the rest on the system untouched. Its mass would automatically influence every single object which comes close to it. Asteroids, comets near its path would change their course. Even other planets are affected. A rogue planet entering a solar system will change that system. But this would be a slow thing, because it would months or even years to pass through thy system.