It's a fantasy role-playing game.

DM: You are Caduceus Clay, a firbolg cleric . You are the member of the famous group of adventurers. Previously, Nott says she thinks its 50-50 Fjord is going evil and suggests Caleb be ready to restrain him. Fjord casts Underwater Breathing on the group and they descend.
DM: It's clear water, so the light does carry further, and you guys aren't going as deep. You do manage to make out, as you get further and further down, the general shape of the tower within sight. It is comparatively murky because of the lack of light, but you can see the shape. You can also, based on the warning that Caleb had given, see some of the figures. You see about five of them, all tangled or wrapped in threads of this seaweed. Regular seaweed, not the strange crimson type that you came across in the Diver's Grave.
Player: I'm going to do a little ping of Eyes of the Grave, just to make sure there's no more of them in this other than the ones we can see.
DM: What's the range on that?
Player: 60 feet.
DM: All right. You're going to have to get pretty close to try it.
Player: I know that we're heading-- once I feel like, or maybe I should hit it again--
DM: Okay, as you swim down to get within range to use your Eyes of the Grave, thankfully, the nearest creature doesn't seem to notice your approach. It is not undead. Make a perception check.
Player: Come on. Ah, better. 20.
DM: Actually, roll at disadvantage because you don't have darkvision, unfortunately, and you're low enough now where the light is limited.
Player: 16.
DM: 16's still okay. Now that you have a better look at it, at a closer perspective, the humanoid creature-- no clothing. It is thin. The limbs are a little stretched, but there are tiny fins at the edge of the arms. Along the sides of the head, there are gills. It has a strange glance, looking around like a sentry, almost. It's not undead. It appears to be more of a fish person.
