I've been considering this idea for a while, but there's a lot to it and I'm not 100% sure whether this would work as an SCP. So, to make sure I'm not barking up the wrong tree before I start writing it out, I'd like to offer up as brief a description as I can manage. Scrutiny and feedback would be greatly appreciated.
There will be three parts to this SCP. Firstly, an unstable two-way portal located in a large, abandoned warehouse. It opens and closes at sporadic intervals, so it is not always accessible. On the other side is another planet/dimension (I haven't settled on this yet) on which the dominant species is very similar to humans. The entire planet is covered in thick clouds which blot out the sun, meaning the only life which survives is nocturnal, and feed either off each other or large root-like organisms which thrive off the heat from the planet's core and extend up to the surface.
The second part would be a community of these humanoids, who originally opened the portal looking for a way off their planet, as it was no longer suitable for their survival. They explain to the foundation that they are the only surviving members of their species to the best of their knowledge, as every other attempt to open a portal ended in disaster or didn't remain open long enough to allow everyone through.
The third part would simply be the collective designation for the main creatures which still exist on the planet, ranging from the harmless herbivorous species to more dangerous carnivorous ones. Part of the containment procedures involves setting up a camp on the other side to engage anything hostile which tries to cross through, along with a number of armed guards on this side as a failsafe, to catch anything the others miss.