This is too cool and advanced for the Tavern, lol.
The Irukandji is the most venomous jellyfish in the world. If you're stung, you'll die within 30 minutes. You can barely feel the sting, if at all, and it injects an extremely small amount of venom.
Ever hear of Humbolt Squids? their as numerous as crabs in the ocean. And thats alot and these things grow to the size of a man, often hunt in groups, and have been known to kill people. Even sharks are being out manuevered by them.
The thing is, many of the Deep sea fish, can't really harm us. A in truth, we could just grab these things and snap them in half of we wanted to. Not to mention to just grab them and swish them up and down really fast, they will pop because of such rapid pressure changes.
But we can only go down that deep with subs, and special suits. and these suits are like tanks also so we have nothing to worry about. I work on a trawler, and I deal with Humbolts here and then. They arent that bad. All you do is you get a harpoon, and impale it. They live mainly in the Pacific, but there has been some sneaking over to the Caribbean.
I saw something on national geographic about jellyfish like these. One guy got stung, somehow knew he had been, and drove himself to the hospital. As soon as he got to the hospital, he became paralyzed from the venom. The doctors saved his life, but that has to be scary.