As per the title. As a xenomorph fan, I'm immensely curious if we know what the thing on the cover of Planar Adventures is? Haven't seen anyone else ask, and I've searched. I'm prepared to feel stupid when someone enlightens me.
Aha! Much thanks, friendly neighborhood T-Rex!
What he said! ^^^
Also, if you want Xenomorphs, then you need to check out the Hive in Horror Adventures!
It's an astradaemon. See Bestiary 2 for more details.
I'm still giddy, overjoyed, and delighted over that cover btw! :D