The Dreadnautilus is a miniboss that you can face in Terraria after turning the world into hardmode. Luckily, it will never spawn naturally, meaning you do not need to fear a large flying mollusk from spawning and murdering you. You will have to spawn the Dreadnautilus yourself during a blood moon event. Killing the Dreadnautilus will award you with a chance at the sanguine staff, a weapon for summoners, or general fishing benefits, or even just cosmetic features. This guide will show you how to spawn the Dreadnautilus, the behavior of the Dreadnautilus, and what drops you can expect from it in Terraria.
In a Nutshell
The Dreadnautilus is an elusive miniboss that you can attempt in hardmode Terraria. You have to fish it up during a blood moon to spawn it, but if you are playing as a summoner, you will want to ensure that you attempt to kill this mollusk as it will drop a good summoner weapon. While it does drop other items, they are largely impractical and can be skipped. The only thing to consider for the Dreadnautilus is the Sanguine Staff.
The first thing you will want to do is ensure you have a decent fishing rod. To increase your chances of reeling in the Dreadnautilus you will want to use the chum caster. This fishing pole will double your chances of reeling in enemies while fishing during a blood moon. If you have not found it yet, try fishing during a blood moon and defeating the wandering eye fish and zombie merman you can fish up.
After you have a decent fishing rod, you will want to wait for a blood moon to occur. You can either force the event during nighttime with a bloody tear, or wait for its natural 11.11% chance to happen each night. Bloody tears are obtained by defeating blood moon-specific enemies.
After you have successfully gotten a blood moon to occur, stand above a body of water and fish. Using a sonar potion will inform you if the fish on the reel is an enemy or not, but there is no way other than using the chum caster to increase your odds. You can reel in a blood eel, a wandering eye fish, blood squid, hemoglobin shark, and a zombie merman in addition to the Dreadnautilus, so it may take a few events to get the mollusk to spawn successfully.
Also consider that the Dreadnautilus will despawn at dawn (4:30 am). Try not to fish close to this time if you are hunting the Dreadnautilus as it will simply float away.
The Dreadnautilus is a miniboss so expect a decent fight. It will charge at the player for about 3 seconds, so ensure you have decent mobility equipped to avoid its contact damage.
It can also retreat into its shell and spray red projectiles at you aggressively. On top of this, it will begin to reflect many projectiles back. During this stage, it will take no damage, and the reflected projectiles can damage you.
The Dreadnautilus will also spawn some blood squids to attack you during this fight. Use this as an opportunity to deal damage to the mollusk and get away before the blood squids close in on you.
The Dreadnautilus will only drop one weapon. It is the Sanguine Staff, which will summon crimson-red bats to attack your enemies for you. They will fly towards your enemies to deal contact damage, and return before flying out again. It is a powerful weapon mid-hardmode for summoners to obtain. Consider grabbing it even if you are not a summoner as you get one free summon anyways.
The only other drops the Dreadnautilus provides are chum buckets, which can be obtained from other fished up enemies during a blood moon anyways. The more important drop to obtain is the blood moon monolith. While it is purely for cosmetic features, you can consider this the trophy drop of the Dreadnautilus as this is the only way to obtain the blood moon background effects other than waiting for a blood moon to spawn naturally.
To spawn the Dreadnautilus you will need to fish during a blood moon. The Dreadnautilus only has a 10% chance to be reeled up, but you can increase this chance by fishing with a chum caster. While it does not exactly benefit its spawn chances, it increases the odds you fish up an enemy rather than a normal fish. To speed up the process, consider using a sonar potion and only reeling in your line when you see an enemy, or specifically the Dreadnautilus show-up.
You can expect a blood moon to naturally occur every night at a 11.11% rate. Roughly a 1 in 9, but if you want to you can force a blood moon to spawn by using a bloody tear. Since this item only drops from blood moon specific enemies, it does not help with getting more blood moons to spawn immediately. You will just have to remember to make use of the blood moons that naturally spawn to make the process involved with hunting down the Dreadnautilus easier.
Congratulations, you now know how to spawn the Dreadnautilus, the behavior of this miniboss, and what drops you can expect from the mollusk-like enemy. This miniboss can be tackled as soon as you enter hardmode, but you ought to wait until you have decent enough weapons to take it down. Since it is just a miniboss its health requirement is not too high, but the chaos of the blood moon can interfere with your hunting process. Remember that other enemies also have a chance to spawn during a blood moon and many of them require quite a high damage output. Be safe and consider using a sonar potion to make the process easier.