[@Dark Cloud]
Don't worry, I'll reign in my autism :D

I'm not completely sure yet... 
An option I was thinking of: A race of little grey alien men who crash-landed their ship into the planet and got total amnesia. That seems like it might be fun, but sorta min-maxy into intelligence (they'd be total wimps physically). The spaceship they got here on would be destroyed somehow, or inaccessible (probably below a very deep lake or something), so there's no advantage from it. They'd start out same as everyone else. 

I also like the idea of the shroomers from that RP, or maybe something arthropod-ish

*Maybe not total amnesia. Maybe they sorta have an idea of where they came from, and it forms their sort of founding myth, around which a religion/culture/society can form. They would likely be very arrogant