This is the forum for helping you out if you're stuck in Grimrock 2 or if you want to discuss about the mysteries of the Isle of Nex. Warning: forum contains spoilers!
So, I ended up doing this game in, apparently, the very, VERY wrong order. Right after I finished the Keelbreach Bog and Herder's Den areas, I took my nifty new Serpent's Staff and went to the Pyramid of Umas, because it had snakes in front of it. I did fine within the pyramid, for the most part (a couple game-over screens in the room with 2x Gorgon and 4x Snakes, but I managed it), but then I got to the Barren Desert. Needless to say, with my level 7 characters and poor gear, I couldn't handle it. Thankfully, I managed to escape, if barely.
Here's the important part:
SpoilerShow
Upon returning to the desert after clearing a couple other areas, I was finally able to take down one of the massive golem things. Score! A Power Stone! ... The other golem, however, completely vanished. Is my game screwed? Do I have to start over? Has this happened to anyone else? I'm assuming it's a serious problem if one of the Power Stones plain isn't in the game anymore.
The other golem doesn't have a power gem, it drops the meteor cuirass and a gold key. Most likely, it didn't vanish, but you teleported on top of it; teleporting onto a monster instantly kills it. If you have the meteor cuirass, or find it on the ground in the desert, that's what happened.
Sweet! I did find the Meteor Plate (the body piece) lying on the ground with a gold key, but it was WAY far away from the teleporter. It must have instagibbed from some mummies when everything spawned upon my return.
I've been running around aimlessly in the desert for ~30 minutes waiting for a reply, because I didn't want to continue if my game was screwed. Thank you!