Underwater Bestiary [Monster Thursday]

It's pretty terrifying out there in the real world. I don't know if you've ever just put your head under the ocean and looked around, but there is some really creepy stuff down there. Fish come in all sorts of shapes that they really shouldn't. Some have lanterns stuck on them, others have way more teeth than they are allowed, and others look like beautiful plants until they paralyze you and feed on you while you are still alive. To be honest, it must suck being a fish. Everything is trying to kill you, and I can't believe anything lives for more than an hour beneath the waves without something trying to kill it. Let's bring that over into D&D!

Giant Sea Anemone (CR 3) Apparently these aren't plants - just horrific animals that look like terrestrial anemones - which are plants. It's confusing. 

Giant Sea Scorpion (CR 4) It's not actually a scorpion... plus it's been dead for millions of years on earth, but there's no reason why you can't kill your characters with one. 

Giant Viperfish (CR 1) This is one of those fish where you wonder where life messed up. Its teeth have grown so large that they can't actually close their mouths anymore, which is a weird place to evolve to. 

Gnathiid (CR 3) Isopods are weird and creepy, and I've been staring at them a lot. I've created an advanced race of isopods that have shunned magic and have put all that focus into technology and science. They utilize water in their machines and inventions, powering their cities with hydro-power.

Grindylow (CR 1/4, 2) Horrific goblin-octopus centaur things, they are vicious and cruel, much like the goblins on land. They enjoy causing harm and hurting other creatures, it's no surprise that they have a sliver of a connection to the ancient ones who reside past the stars. They're just waiting for a great grindylow leader to help them rise up against the sea-folk like sea elves, tritons, and even sahaugin.

Plated Guardian (CR 19) I may have recently watched Atlantis: The Lost Empire (2001) recently, and really wanted to recreate the guardian in that movie, but as a beast. For far too long have beasts been given the short stick in D&D, and I think several monsters should be pretty powerful just because of their size, their strength, and more! For those who don't like a high-powered beast, there are also rules on transforming it into a construct while retaining its current Challenge Rating.