Dreadnautilus

There is no summoning item and it never wanders in by itself. You fish it up. During a blood moon a cast can hook an enemy instead of a catch, and this is one of five things that can come out of the water on those nights. It is by far the scarcest of the group, so expect a long run of eels, sharks and mermen between sightings. The pool does not have to be natural, and a Lifeform Analyzer will call it out once it is in the water.

A Sonar Potion is close to mandatory. It names what has taken the bait before you reel, so you can throw back the rest of the blood moon roster and only commit when this one bites, and the warning buys you the seconds to drink buffs and back off the shoreline. A Chum Caster raises how often blood moon enemies bite at all. Run both and one night can produce several fights instead of one.

Two things to know before you start. It will not wait for you: if dawn arrives while it is still alive, it flies off and the fight is over. And nothing stops you hooking a second while the first is still swimming, which is a much worse idea than it sounds.

Every attack opens with the same pause, and the direction it faces during that pause is the tell. Turned away from you it is loading a dash. Turned toward you it is loading a spray. Learn that one detail and the whole fight becomes readable.

It winds up facing away, then comes at you, and once it arrives it circles rather than passing through, so running in a straight line keeps you inside it for the whole attack. Break the line instead. One sharp change of direction out of a hook, a set of wings or a dash accessory such as the Shield of Cthulhu throws the tracking wide and the rest of the charge whiffs.

The wind-up is the part that punishes carelessness. While it is charging up the dash it bounces projectiles straight back at you, so a held trigger feeds you your own bullets. Stop firing when it turns away, start again the moment it moves.

Facing you, it fires three quick bursts of red and kicks back after each one, which fans the bursts apart instead of stacking them in one place. It reflects nothing during this attack, so that is your damage window, and it is where most of your fight should happen.

When it flushes crimson it hangs tears in the air nearby and each one opens into a Blood Squid a moment later. It only reaches for this attack when you are reasonably close, and the tears need open space with a clear line to you, so a boxed-in arena denies them somewhere to land. That trade costs you the room you need to break the dash, and most people would rather have the room. Squids are minion work: the Blade Staff is the standout because it goes straight through their armor, and letting summons handle them keeps your own damage on the main target. Hooking a second Dreadnautilus raises the squid ceiling as well, which is the real argument against fishing while one is alive.

The rotation is scripted and it loops, so after one attempt you can call the next move without looking at it. It leans heavily on the spray, drops the dash in between, and only reaches for the squid summon twice per cycle. Once you have the sequence, the fight is about where you are standing rather than how fast you react.

• Ichor, easiest from a Golden Shower, because its armor is the reason your damage feels low.
• Homing weapons such as the Spirit Flame, which spare you from aiming at a target you can barely see.
• Light. Night, red rain and red projectiles overlap badly, and Shine, Night Owl and Hunter potions each solve part of it. Turning blood and gore off swaps the red spit for pale clouds, which reads better in the dark but hides projectiles inside the cloud.

It fights like a boss and is filed as an enemy. No health bar across the top of the screen, a banner rather than a trophy, and no relic on Master. Re-Logic went back and forth on the question during development, to the point that a trophy was drawn before the idea was shelved. The bestiary entry and banner do arrive after far fewer kills than a normal enemy asks for, which is the game quietly conceding the point. The name welds dreadnought, the early twentieth century battleship, onto nautilus, the shell it wears, and it went by Blood Nautilus in the pre-release trailer.