YMMV / We Need to go Deeper

• Demonic Spiders:
  • Time Devourers, very deliberately designed to end your run by being too fast to outrun and able to rapidly eat through the submarine's health while taking multiple torpedoes to destroy. Even then, they'll split into more Devourers and a new one can spawn in before you've killed the first.
  • Barnacle maws. They have more health than most enemies and hit hard, but what makes them so dangerous is how nimble they are on top of it. Most enemies will overshoot the sub and need time to turn around to attack again, providing an opportunity to put some distance between them and the sub, but barnacle maws can keep pace with most submarines unless you're going at maximum speed and will continuously inflict damage. They also tend to spawn at least two at a time.
  • Mechanical emissaries, the defenders of the Ambassador boss. Very high health, and with a shotgun that can destroy doors as they try to kill you, which spreads water from leaks. They can actually be destroyed without much difficulty by getting up close, as their gun can't hit you if you're in the middle of their body, but more than one might attack at a time and the interior fight will be going on during a boss battle.
• Game-Breaker: The harpoon gun, which deals high damage and has enough knockback to hold enemies at bay. The Volcanic Depths are especially affected, as the harpoons can pierce the armor of the enemies there, letting you take out even a volcanic turtle with just a few hits without needing to target its weak points. If the turret is getting two of the energy units, it can even hold back a Time Devourer.
• That One Level: Of the various biomes, the Infected Depths is arguably the most dangerous. In addition to the threat of barnacle maws mentioned above, hull breaches are more dangerous than other biomes because they can lead to barnacle spiders spawning in the sub with numbers seemingly having no upper limit, overwhelming the crew if the leaks are in more than one room. A single barnacle grabber, which creates four holes around the ship, can easily doom the expedition.