Theme: Most of the backgrounds would have an habit of speaking with a specified environment. If you're looking more in the vein of classes, races and mechanics, take a gander at the best D&D sourcebooks. Any humanoid that starts its turn within 30 feet of the hag and can see the hag's true form must make a DC 11 Wisdom saving throw.
Spiritualists of the past, who claimed to be able to speak to the spirits and ghosts of the beyond, would use sleight of hand and simple tricks to create illusions to deceive and thrill their audience at a There are many monsters that can be found within specific locations such as the underdark or within aquatic depths. This part is pretty clear to me: the weird remains inside the tank until summoned, and the source of water for the weird is the water within the tank. Rangers are an unusual type, which, when you think about it, is something you could say this about pretty much D&D 5E class.