Sanguine Staff should be S rather than S+. Yes it has a very high damage output and the best AI of any minion in the game, but getting it is a pain and is very time-consuming.
First you have to wait for a Blood Moon, which could take hours and hours of continuous sleeping. Then you have to fish up the Dreadnautilus, which could take a while because of all the other fish and enemies that could be fished up. Then you have to kill it, which is way easier said then done. If you move around too much, it'll hit you over and over again with its circling attack and if you move around too little you'll probably get hit by its blood projectiles or by its Blood Squids.
And if you don't manage to kill it before dawn, or you die, you'll have to wait for a natural Blood Moon again if you didn't get any Bloody Tears. Furthermore, there's only a 50% chance of Dreadnautilus dropping the Sanguine Staff on Classic worlds, so you might not get it if you're unlucky.
This is a pretty ironic post, isn't it (since my username is Dreadnautilus5000).