I wanted to have some Shuttle bugs living near my base to keep it clean, so I used the terraformer to carve out a natural-looking cave, and made sure to make it down-current of my plants, so that any decaying plant matter would collect in the caves, attracting Shuttlebugs due to their love for eating decaying organic matter.
Within a couple of days, I had a few Shuttlebugs living in the cave, and a few days later, I entered into the cave to see a few round, dark greyish-purple eggs, similar in color to most Shuttlebugs, sitting in one corner of the cave. I decided to make the cave go deeper, having multiple caverns within it, and having small, more private areas for Shuttlebugs to mate and lay eggs in.
All this terraforming wasn't exactly sitting very well with one of Subnautica's most mysterious and potentially dangerous denizens. As I continued making the cave go deeper, there was a rumbling sound and the ocean floor shook as some of it began popping up quite a bit, almost like a giant mole was digging underneath the substrate. I could feel each vibration as the bump passed right under me, and as they grew stronger as it approached, and weaker as it ran off. I knew it wasn't a natural phenomenon. There was some sort of creature behind it, and it didn't seem too pleased with me altering its environment.
Eventually, after making sure that nothing was coming back for a second pass, I used the terraformer to slowly and carefully dig a hole in the ridge left behind. What I saw beneath it meant very bad news for me. The tunnel left behind was huge, being extremely long and and almost 5 meters in diameter! It had a primitive, imperfect pattern to the digging marks, meaning that whatever did this was definitely not a machine, but it WAS huge. Judging by the excavation pattern, it was one single creature, not many small ones, that dug the tunnel, and I looked through my database, trying to think of a creature capable of doing such a monumental task. Until now, there were no creatures I had encountered that were able to do such a thing. I dreaded the day I actually met this massive marine mole, and if I never met it, it'd be too soon. Little did I know that I would come face-to-ugly-face with the creature much sooner than never, much to my chagrin.
Over the next couple days, I tried to tone down my terraforming operations, hoping that a reduction in geographic disturbances would keep the giant creature away from me for a while. Unfortunately, my hopes were entirely just that: hopes. Hopes that would go unfounded as I was confronted with the creature. The way I encountered what was behind the tunneling was actually quite frightening: the monster had actually dug a tunnel quite slowly to a spot in the sand, to avoid being seen, and created a small, expandable hole in the ocean floor, almost like a trapdoor spider with a giant, sphincter-like door.
It was unknown exactly how it created its door, but perhaps it was merely something the creature could make from its own body, or that of another animal. It used its digging appendages, which resembled large claws, to stretch out the door's edges, allowing the massive creature to emerge and ambush its prey. My first reaction to seeing its door was to investigate, although cautiously. I kept my stasis rifle at the ready, in case I needed to retreat.
As I approached the door, the giant creature emerged and swiped at me with its huge pincer-like arms. It was quite large, with most of its body still underground, but it was crab-like, with a bug-like body and its excavation appendages resembling tusks compared to the rest of its body.
My heart nearly jumped out of my chest when it burst forth from its lair, and I immediately pulled out my stasis rifle and blasted a 30% strength blast into its face, with the stasis dome being only 30% of its max size and duration. I swam away at top speed, not wanting to face that thing in a "fair" fight. I swam to the moonpool and entered the USS Explorer, loading up on vortex torpedoes for a battle with this "Sandcrab".