(I need a quick break from writing my First Year Progressian report, so here’s something a little silly…)
Cosmic horror and failed stars possibly aren’t the most obvious mix. However, I think there are parallels.
What Man Was Not Meant To Know: brown dwarfs are extremely faint, around maybe a ten thousandth of the Sun’s luminosity. In fact, because they’re so faint, their existence wasn’t confirmed until as recently as 1995 (Gliese 229B). So, they’re a classic piece of ‘what man was not meant to know’. There isn’t a single one that you can see with the naked eye from Earth (unless you’re one of these difficult people who insists on counting Jupiter, of course).
That vague, morbid sense: a brown dwarf is arguably what happens when a stellar embryo has an abortion. They don’t fuse hydrogen (or at least, not in any stable, prolonged way), so they glow through residual heat from their formation. (In technical-ese, they thermalise gravitational potential energy.) According to Burrows et al (2001), they “cool like a rock”. So as time goes on, a brown dwarf gradually fades and dies away, like an abandoned ember, until eventually it will just be a dead ball of frozen hydrogen and helium, drifting lifelessly and forgotten through a darkening universe.
They can be absurdly ancient: all good cosmic horrors are old, long pre-dating Humanity. Metal-poor brown dwarfs in particular are like this. (One of the things in my current candidate sample has an upper age constraint of ~10 billion years, making it potentially twice as old as the Sun.)
They’ll see us off: all good cosmic horrors are largely immune to human agency. Brown dwarfs obviously couldn’t care less about us, and nothing we can currently do can impact on them in any way. Also, although they gradually fade away, the cooling timescales are enormous. A 0.06 M_Sun brown dwarf will take around 1.6 billion years even to evolve as far as T0 . Heavier objects will take even longer. If we imagine a 0.07 M_Sun brown dwarf which forms at the same time as the Earth – so ~4.5 billion years ago – then in 5 bn years time, it will have only got as far as type T6 (surface temperature of maybe ~ 1200 K). Meanwhile, in this time, the Sun will have expanded off the Main Sequence and certainly ended all life on Earth, and maybe even have physically-swallowed the planet.
The complete alienness: lastly, it has to be noted that brown dwarfs are just completely, weirdly different. They’re nothing like the environment we live in. They’re probably even less similar to conditions on Earth than London is to R’Lyeh. Brown dwarfs can range from temperatures where the weather system is made of molten iron droplets to temperatures where it might actually rain liquid water. Their atmospheric pressures are enormous and their surface gravities are hundreds of g. They’re just weird.
 Scientific honesty caviat: this number obviously depends on how far you believe the Tucson et al models. Models of low-mass evolution are still a bit up in the air, in a lot of ways.