A main aspect of Subnautica is its horror elements. After Robinson’s crash lands on 4546B, she realizes she is the only highly intelligent being with the skills of complex reasoning, communication, and spatial analysis. There are hints of intelligent ancient life in artifacts found throughout the game, but the aliens who created these artifacts are nowhere to be found. Additionally, there are hints of a creature with complex emotional thinking compared to that of humans throughout the game, especially late in the game. So, for the majority of the game, Robinson is isolated by herself and must find a way off of the planet while she is surrounded by creatures that act on innate, instinctual behaviors, some of which are not as friendly.

Subnautica divides the planet’s fauna into classes. There are the herbivores, which are typically smaller species, some of which the player can grab and use to consume water and/or food for sustainability. There are slightly larger herbivores that can be defensive but are typically passive. The next class is carnivores, which vary in size from a small, explosive Crashfish to a large Sand Shark, which is slightly larger than a Great White Shark. The carnivores are all aggressive creatures and will attack the player if too close. The next class is scavengers and parasites. The design and behaviors of these creatures parallel that of typical parasites, crustaceans, and jellyfish/invertebrates found in the waters on Earth. This class ranges in passive and aggressive behaviors. The most lethal fauna belong to the Leviathan class. These are the largest living organisms that are found in the game. The Sea Dragon, Reaper, and Ghost Leviathan creatures are the deadliest creatures in the game and can kill the player easily. However, there passive creatures who act as gentle giants like the Reefback and Sea Emporer Leviathans.

The isolation and vast ocean on 4546B invoke thalassophobia, or the intense fear of deep bodies of water, in players. The player not being able to see far in the ocean and then hearing a creature roar invokes the fear that there is something large and deadly, and the player does not know where that creature is until it’s too late. There is a common saying among veteran players: if you can hear it, it already knows you’re there. The nearest Reaper Leviathan to the player is next to the crash site of The Aurora. The crash caused a lot of sediment to be mixed into the surrounding water, making the area murky with low visibility. Hearing the roar of the Reaper for the first time, but not being able to see it, is terrifying. Players then catch a glimpse of its outline in the distance, showcasing its large size. By then, the Reaper is getting closer and closer to the player, and its fast speed can easily outswim the player. If the Reaper catches up to the player, it will eat the player whole, causing the player to respawn back to the lifepod.