Me and friend decided to train friend's managarmr a bit. So I took a Reaper, he took a managarmr and we went off to wyverns' place near green obelisk on Ragnarok. Everything was cool, we were killing wyverns, even killed an alpha. So I kept walking, leaving my friend behind. And THEN I hear him calling for me and for help. So I quickly turn around just to find a frozen golem and a damaged poor mana. Reaper took a good amount of time to put it down. But we did it.
Moral of the story is: never take on a golem alone.
If you are unsure if a rock is a disguised golem or not, a spyglass shows their name and level even when disguised. Also, when disguised, the rocks often move slightly as you get close, re settling onto the terrain.
All rock elementals have the same rock skin when disguised. It is a bright yellow boulder and is very noticeable against dark mountains. Keep your distance, as they can aggro on to you when you get close.