Dreadnautilus

The Dreadnautilus is a Hardmode enemy summoned by Fishing during a Blood Moon. It is one of the five enemies that can be summoned by fishing during a Blood Moon during Hardmode, as well as the Wandering Eye Fish, the Zombie Merman, and the two other Hardmode-exclusives, the Blood Eel and the Hemogoblin Shark. The Dreadnautilus is rarer than the other four Blood Moon fishing enemies, occurring only 1 in 10 spawn attempts (on average), and is also considered the most difficult to battle.

Attacks

 * Spins around the player for roughly 3 seconds. Upon contact, it will damage the player.
 * While this attack is charging, Dreadnautilus will face away from the player and will reflect projectiles.
 * Rapidly fires a spray of red projectiles at the player. During this phase, the enemy will turn invincible.
 * Briefly glows illuminant crimson and summons three red symbols. After a moment, each symbol will summon a Blood Squid, which will attack the player with a ranged projectile.

Tips

 * Summon weapons are useful for handling the Blood Squids while the player focuses on the Dreadnautilus.
 * Using the Chum Caster gives the player a greater chance of finding the Dreadnautilus and other blood moon fishing enemies, this combined with Chum Bucket s will give the player the best chance to find them. The use of Sonar Potions will allow you to skip past other blood moon fishing enemies, letting you fight the Dreadnautilus more over the course of the night.
 * Of the 4 attacks that the Dreadnautilus employs, only the Spin attack will phase through walls, since the enemy itself also phases through walls. A good strategy to cheese the enemy is to build a box and use weapons that can attack through the walls. When you see the enemy charge up for the spin attack, temporarily leave the box and re-enter after the enemy is finished.
 * Since this fight takes place at night (and hopefully not during rain), visibility can be an issue, and can make the projectile attacks quite difficult to perceive. Using a Hunter potion, along with a Night Owl potion and Shine potion, will help with visibility quite a bit.

Trivia

 * Similar to the Sand Elemental and the Ice Golem, the Dreadnautilus is not a boss or mini-boss, even though it has stats comparable to a boss. This is evidenced by its lack of a health bar and the fact that it drops a banner, not a trophy.
 * It resembles a.
 * Its name is a portmanteau of "Dreadnought" (a class of warships) and "nautilus."
 * Its original name was "Blood Nautilus" in an official trailer.