It's a fantasy role-playing game.

DM: You are Mollymauk Tealeaf, a tiefling blood hunter . You are the member of the famous group of adventurers. Previously, Caleb grapples it with Earthen Grasp. It manages to clean the tar off the lens, and breaks Caleb's concentration on the grapple by pinning him against the wall with a blade through the chest.
DM: First strike it dodges; it moves out of the way. The second strike actually makes an impact, so roll for that.
Player: That's okay. (counting) That's 12 points of damage.
DM: 12 points of damage, all righty. Carves through with the second strike.
Player: For a third, slightly less exciting attack. Natural 20!
DM: This is your off-hand, so it's not a magical weapon.
Player: But its magicked up.
DM: Correct, so the extra rite damage is magical, but the actual blade will be halved.
Player: Okay, that's fine.
DM: So roll the d6 for your blade.
Player: That's two to three, so that's five.
DM: Five reduced to two. So two damage plus this, doubled. Well no, sorry, the two is doubled because it was a crit. So it would have been four plus three, which is seven.
Player: So it was a five.
DM: Sure, it's five damage.
Player: And then six because this is doubled.
DM: So 11 points of damage. Now the armor is reduced to 16 as you're carving away at its armored shell. It's starting to look pretty hurt. You see it shifting rapidly trying to figure out its situation and tactically maneuver best it can.
Player: I'm going to see if I can hop back up out of-- am I ever getting out of melee, or am I not getting out of melee?
DM: If you back all the way up to here, you can. Or all the way up to the top.
Player: It will still get an attack of opportunity on me, though. Without disadvantage now.
DM: At the moment, no.
Player: You know, I'm going to stick around for now.
DM: Okay.
