I wanted to share a revelation I've had with you. No, not while trying to classify your species (good guess though), while writing a CoC scenario. D20 is super easy to write for. With the huge wealth of material there is in existance already, when you are conceptualizing a monster and think, "Hmmm... I'd like something horrific for this scence that does X. Oh yeah, this would be like that other monster that is from this suppliment." and you've already got the stats.
It's pretty nifty.