"A really good follow-up post to this one would be Non-threatening Cosmic Monsters. Or at least, monsters that don't kill you. Can you write a monster that would horrify the players without threatening them? (Of course you can. That's why this is such a good prompt.)"
So here's my version of that follow-up, some non-threatening cosmic monsters:
Looks like a spindly growth of coral, or maybe a desiccated cactus. It might stand a little taller than a tall man, or as tall as a two-storey building Around it swarms a cloud of gnats (though on closer inspection these "gnats" don't look any clearer than they did at a glance, just spiny black motes flitting about). They pop up in places a hunter might set their trap, if that hunter was comfortable treating humans as game. Near watering holes. Along well-trod paths. Just around the corner.
HD 3 AC as leather
Move - Int - Mor -
Sampling Swarm - Any animal passing near an utulbor will attract its "gnats", which proceed to take minuscule, harmless samples of their tissues. One round later the things will return those samples. One round after that a partial clone of the organism the samples were taken from will sprout in the branches of the utulbor. If that clone has anything approaching a functional throat and lungs, it will be screaming.
Crofter's Crop - When an utulbor is encountered there is a 1-in-6 chance that the Crofter will be there harvesting its fruit. The Crofter is not a non-threatening cosmic monster.
A mound of something like frog eggs that contain nothing but more frog eggs (and so on further in as deep as your eyes can make out). The three-dimensional membrane of a hyperspatial appendage dragging through our little slice of reality. Usually found underground, closer to the center of this planet's gravity well. Usually. They tend to ooze around within a set territory, and never attack or even react to outside stimuli except to expand.
HD 1 (at first) AC as flesh
Move as snail Int - Mor -
Spill The Higher Flesh - If an attack strikes a diralac but doesn't kill it the diralac splits open, releasing a torrent of its greater substance into this world. It doubles in HD and size. Its mass increases at an even greater rate. There is no limit to how many times this can happen which would matter on a human scale. Maybe restrict it to something like "slashing and piercing attacks" if you don't want the first diralac to flop into a puddle of acid to overgrow the solar system.
Lacey, chitinous fingertip patterns in smoky blue and indigo, floating in graceful spirals along a geometric track. Wherever their edges touch they'll trace esoteric marks, shallow enough that even on bare skin the marks will barely bleed. They appear without warning, and when their dance reaches its unpredictable end they'll shrivel to razor-sharp dust.
HD 1 AC as chain Prolonged Contact 1 dmg
Move as waltzing human Int ??? Mor 11
Alien Artform - The continuous marks left by the whirling calligraphers are just shy of being nonsensical. There's enough of a pattern to them that the automatic part of the human brain can latch onto them, start to see depths of meaning that would make the greatest poets weep at the shortcoming of their works. This meaning never resolves enough to mean anything in particular, always skirting just beyond conscious recognition.
Deranged Devotees - Most people are able to shrug this off, in the same way most don't stop to admire every rainbow. Others get obsessed. The more impulsive ones will trail behind a calligrapher, poring over every last curlicue until they die of dehydration. The more possessed ones will apply their resources to collecting all the calligraphers' marks they can, paying through the nose or even killing to get them. News of a "virgin" calligrapher, without any devotees, can spark a violent goldrush among these collectors.
Diaphanous beings of elegant complexity, like jellyfish folded into origami. They flock to places where other worlds meet this one, to portals, summonings, thin planar barriers, and suchlike. They linger for a time, probe at the boundaries, and then they go on their way. Their movements seem sad to human observers when they leave, so silent and so slow, hence their name. They're said to be yearning for a way home. This is the projection of familiar emotions where none exist.
HD 1/2 AC as plate (partially insubstantial)
Move as owl Int 10 Mor 6
Partially Insubstantial - Glumgliders are made of something besides earthly matter, or maybe most of them is somewhere else. In any case, the effect is that they're partially insubstantial. This grants them an armour class equivalent to plate, and the ability to squeeze themselves through solid objects that are less dense than stone.
Rifthound - Glumgliders have a sixth sense for connections between this world and another. Maybe it's their only sense. If encountered they'll either be headed towards one of these connections, or drifting away from one after lingering there. The rare few who know how to summon glumgliders use them as hunters of summonings and the like.
The Thousand-Petaled Eye, by tradition a singular entity, though this is just conjecture. Kyudka appears in the sky above important events, and it's said that the things its "pupil" focuses on are bound to be key players in these events. That Kyudka's mere presence is enough to spark existing tensions into important events doesn't get remarked on often enough.
HD 20 AC as chain (if you can reach it) If It Were To Ever Fall To Earth 10d6 to everything within 50 meter radius below, max damage unless save vs. breath is passed
Move as blimp Int ??? Mor -
How Are We Going To Get All The Way Up There? - The lowest Kyudka has ever been recorded to appear is 5 kilometers up.
What follows the coming of the Thousand-Petaled Eye? -
|D10||What Hath Kyudka Wrought|
|1||Mass hysteria, group suicide pacts.|
|2||Hastily brokered peace between feuding factions.|
|3||Wild abandon, orgies in the streets.|
|4||Forgiveness of debt and crimes.|
|5||The rise of a charismatic cult.|
|6||The coming of a fell wizard and their cauldron-born armies.|
|7||The unveiling of secrets and conspiracies.|
|8||Asceticism, the forswearing of wealth and earthly pleasures.|
|9||Witchhunts, purging the scoundrels revealed by the Eye.|
|10||A migration of monster slayers to bring down the Eye.|