Rock looking jelly esque enemies.
Just wanted to make sure if they've always existed or if they were new. Saw them yesterday for the first time. The game doesn't seize to surprise -_-

I think they can show up in any scarlet fortress, and rarely in any place that has stone blocks.
They're "supposed to" camp amongst breakable stone blocks to surprise you. They're rare spawns, though.
There are a few guaranteed spots to see them in Scarlet Fortress, especially Grim Gallery. They won't bother maintaining the "I'm a breakable block, I dare you to try hitting me" illusion there.

They are a bunch of stalkers is what they are. I've seen them everywhere and as starlin mentions any place that has stone blocks. The latest sighting was at FSC doing a vanaduke run. Was trying to heal then the block... came alive... lol. Enjoy.
I belive a normal place to see them is in tier 3 scarlet fortresses or something.