Reg has light brown skin and dark hair. He wears a metal helmet with two asymmetrical horns protruding out of the sides and what appears to be a glass lens in the front, which, according to Nanachi's theory, displays the number of Incinerator charges he has left to use.

Underneath his helmet is a jagged metal headband of some sort, with bolts on either side keeping it in place on his head. His ears are slightly pointed. Reg's eyes are yellow, and his pupils are catlike, vertical slits. There are two red patches of skin on his cheeks, and four more on either side of his rib cage. His eyebrows are small and gray. Though he is a robot, the only parts of him that appear to be mechanical are his arms and legs, which are bulky compared to the rest of his body. He has nipples, a belly button, and even human genitals.

He is usually shirtless, save for the tattered red cape he is wearing when Riko finds him. His washed-out green and purple pants are baggy and stop just below his knees. The buckle of his belt resembles an eye with a long slit. In the events transpiring at the Ido Front, Reg loses his right forearm while Umbra Hands run tests on him and earns a scar on his belly button after his fight with Bondrewd.

In an encounter with a Turbinid-Dragon, in which he blocks a strike from the creature, Reg's remaining left arm gets chipped leaving a small scratch on his left forearm. He is later equipped with the Artifact Gentle Knock which is attached in place of his right forearm.

Source: Made in Abyss Manga: Made in Abyss Chapter 3-4, 29, 31, 37, 43, and 63 | Made in Abyss Anime: Made in Abyss Episode 1

Incinerator

The Incinerator (火葬砲: Cremation Cannon) is a powerful incendiary cannon built into Reg's hands and feet, emitting a beam of light, indicating the area to eliminate, penetrating through objects. The size of the beam changes depending on Reg's will

Extendable Arms

Reg's arms can extend up to 40 meters each. He can shoot them to the top of cliffs or grab things very far away. The cord attaching them is very durable and appears to be made of countless metallic threads. Using these arms does not reduce the pattern on Reg's helmet because they require a minimal amount of energy.

Heightened Senses

Reg's senses of smell and hearing are stronger than that of a human's. Nanachi has commented to that he reminds them of a dog by the way he follows his nose.

Super Durability

As commented on by several characters, Reg's body is extremely durable. Despite his high durability, Reg is agile and weighs little. His wounds heal at a faster rate than a human's, and he has a very high pain tolerance. His navel is the thinnest part of his skin, making it a weak spot.

Source: Made in Abyss: Official Artbooks | Made in Abyss Manga: Made in Abyss Chapter 7, 16, 18, 34, and 37