Ignoring how they're misused, an 'unknowable' deity can work wonders in your setting. A God who is truly a higher being, detached from concepts such as mortality, morality, linear time and three-dimensional space.
If you're going to use a cosmic horror themed deity, be willing to accept the consequences! Everything in your setting feels a little less important when it's contrasted to the uncaring whims of the infinite void, and "
your characters are just flotsam in the tides of fate" isn't the sort of mood you want to set in a heroic adventure full of PC empowerment! Settings like
Arnold Kemp's
Centerra (sorry I'll try and stop leeching off them eventually) thrive in an endless fractal nightmare of billions of concentric, pointless conflicts. Settings that want to focus on individual heroics and triumphs will feel a tad undermined by that sort of thing.
Also, in a touch of irony, a setting such as 2011's Dark Souls with a central theme of "player struggling to hold onto the last few embers of light left in a dying world" would actually be made less bleak by the introduction of gods beyond time and space, since that would mean that the end isn't inevitable everywhere, at least not yet.
PUTTING THESE ENTITIES IN YOUR SETTING IS NOT A THROWAWAY DECISION.
Some of the most interesting uses of 'eldritch-adjacent' themes (in my opinion) are seen below.
Doctor Manhattan in all his blue glory.
Minor spoilers for Alan Moore's Watchmen. As you can see, Doctor Manhattan's not crazy or tentacular or horrific. He's just blue and (mostly) naked. He's a comic book superhero. Jon gained powers after a freak lab accident, took up a cool codename, and fought evil. He's got a pretty basic suite of powers, like
flight, the ability to make
copies of himself, complete
invulnerability,
reality alteration, the ability to see all of
time and
space at once, and can
rearrange individual molecules into anything he wants.
We have an entity that can see all of time and space at once, and change it according to their own whim. This entity can never die, be anywhere at any time, and can change any given piece of matter into essentially any other piece of matter. They could seize complete control over everything in the known universe and subjugate all sentient life, but just have
better things to do. Oh yeah, and they used to be human, and their former relationships and perspectives are clashing horribly with their new existence.
I wouldn't recommend putting something like this in your game; they're just too powerful and too likely to derail the story to the detriment of everything else. They might make an interesting antagonist or 'force of nature' to contend with, however.
I'm going to cheat and just link directly to the article on
Goblin Punch that introduced me to this idea. Thanks Arnold!
For those who don't want to check out one of the best OSR writers I've ever read, the summary is straightforward:
What if the universe is just a petri-dish from some higher being? It acts upon us in macroscopic ways our microscopic selves simply can't perceive, to complete an experiment that only makes sense to macroscopic beings?
This is very much the 'classic' eldritch abombination. A creature that acts on a scale incomprehensible to humanity, and ignorant to the suffering they cause to us. A real-world analogy would be bulldozing a termite mound to build a cricket pitch- the termites have no concept of bulldozers, and would be completely incapable of understanding cricket. Oh yeah, and the destruction of the termite mound would simply be a side-effect of the cricket pitch's construction.
Harbinger, a recurring named Reaper.
Minor spoilers for the Mass Effect franchise. These guys aren't actually 'eldritch horrors.' They're big, their machinations span hundreds of thousands of years, they possess technology beyond understanding, they're physically imposing, etc. They're also very certainly
not any sort of 'higher being.' Their technology is bizarre and advanced, but obeys the same physical laws as everything else. Their arrogance leads them to make fatal mistakes. Finally, we eventually learn their 'incomprehensible' morals...
To breed. Just like every life form from bacteria, to mammals, to Turians and Asari.
These guys can end feeling like a cop-out to your players, if you've built them up as 'beyond comprehension' and reveal them to just be 'normal' and capable of being killed in a boss fight. Use with caution.
A Caryll Rune, representing Formless Oedon.
Minor spoilers for Bloodborne. 'Great Ones' exist outside of our world, but intersect with it in some ways. They are alien, even to experienced scholars. The Eldritch Calamari Special space gods of the Bloodborne setting are neither malevolent or dismissive of humanity- they're
friendly. Many of the most twisted nightmarish places, scenarios and creatures in the setting aren't caused by malice, they're a direct result of people trying to understand and emulate these creatures.
This is a more personal horror than a traditional eldritch evil, seeing that the actual pain & suffering come from the actions of people and not the whims of a god.
So there's 4 things that I think make excellent use of the classic cosmic horror themed trope of 'unknowable entity from outside our reality that exists outside of our concepts of life, death, matter, space or time' in one way or another.
I've probably missed some great cosmic horror stuff, but I'll let it lie for now.