Let's come up with an amphibian race!

You've come up with a great idea regarding the dark elves!! You logically linked the hydras leaving the underwater realm and their encounter with the dark elves!! Now, it can be said that the underwater race and the dark elves are fierce enemies. Regarding the symbol... you actually already mentioned a kraken entwined with seaweed. This structure will appear in castles upon finding the Grail and provide the ability to emerge from underwater at any level, as well as move across land at the same speed as underwater. We talked about this, and it's good.