Originally pulled from Legends lore, the cortosis that is used for the Stranger's helmet and gauntlet is a rare ore that has the ability to disrupt lightsaber blades. Despite its protective qualities, it's not as durable as beskar.
In-universe, cortosis can temporarily short out a lightsaber to disable an attacker, but does not permanently damage the blade. The energy absorbing effect the helmet and gauntlet briefly take on matches the color of the lightsaber blade affected.
Creator Leslye Headland has said the paired episodes of "Day" and "Night" were inspired, in part, by Alien (1979) and Predator (1987).
A group of umbramoths is called an eclipse.
The trunks of the trees in the umbramoth grove looks strikingly different from the previous episode due to the mass hatching that takes place during the night.
The Stranger uses a style of lightsaber combat called Tràkata, turning the saber on and off during combat.
