Squid

It spawns on its own in the ocean, down near the seabed, and it is rare enough that you can play a whole world without meeting one. There is exactly one reason to look: it always leaves ink behind, and that ink is the only route to black dye at a dye vat. If nothing in your wardrobe needs to be black, this is an enemy you can ignore forever. A Lifeform Analyzer will tell you when one is nearby, which saves a lot of blind swimming.

Underwater it jets at you in short bursts and is genuinely awkward to hit. Out of water it cannot move or chase at all. Pull one onto the sand and it is a free kill with no risk attached. It also skips the electrified state that expert gives the other jellyfish-style enemies, so the water around it stays safe.

Run the usual spawn boosters and bring something that solves the breath meter, since you want to sit at the bottom rather than making panicked dives. A solar eclipse is a surprisingly good window: it pushes the spawn rate close to blood moon levels, and its own monsters cannot appear in water, so they stay stuck on the beach and in the caves under the sand while ordinary ocean life pours in much faster than normal.