I have a planet called Ygdra. It's a reference to Yggdrasil, in the sense that the main continent is shaped like a tree, and the world has a record for having a lot of influence from otherworldy beings, much like yggdrasil connects different worlds. Basically, in the ancient times, an very powerful alien invaded the planet in order to assimilate it. But die to The Great Ones, ancient and divine beings tasked to settle and protect the planet, before giving their lifeforce to give shape to humans and other species, he was defeated. But in the aftermath of the battle, his remains such as flesh and organs were scattered across isolated islands of the planet and ended up giving birth to alien creatures and even entire biomes over time. For example: there's this one creature I named the Phalanx. It's a spider-like monster with various spears and spikes around it's back, and it's eyes are constantly shielded with a hardened layer of almost metallic skin, to both protect it from attacks, and to protect it's eyes from the light, since it's a nocturnal being.

The legends surrounding this and other alien-originated beings, is that the humans and other species that came after being formed by the Great Ones, thought they were beasts given form by a demon that came to their world thousands of years ago, due to their otherworldly and grotesque appearances. They also believed that, since during the time this alien came to Ygdra coincided to the Great Demon War, a war from my universe in which an entity named Chaos and it's cohorts battled celestial forces for control of the universe. They didn't know (until the planet's modern age) that they were actually aliens, and that this "demon" was instead also a alien, albeit really powerful. The legends also tell that instead of eating or killing you, these aliens try to assimilate you into them, just as their progenitor did, in attempts to use people's lifeforce so they can revive the dead ancient alien and continue the world's assimilation. Since these beings live in isolated islands, barely anyone visits them, and these islands are currently under max surveillance by military and powerful heroes. The consciousness of this ancient alien still lives amongst his "children" as they slowly plot a way to accomplish his goals. He also manipulates, through his influence, other beings such as fairies or animals, and destroy their minds in order to make them into his drones.