Profile
Appearance
Like Toriel and Asgore, Asriel is a Boss Monster with white fur, long ears, a snout, and a set of visible fangs. In his child form, he lacks horns and has a small tuft of fur atop his head, unlike his parents. He wears a green long-sleeved shirt with yellow stripes and black pants, similar to the first human's clothing.

God of Hyperdeath
This form is named directly in the game. During much of his battle, the "Check" option labels Asriel as "The Absolute GOD of Hyperdeath!" In this state, in contrast to his child form, Asriel has black sclerae with white slit pupils, longer fangs, a pair of horns, and black markings on the sides of his face. He wears a long robe with white sleeves and the Delta Rune symbol, akin to Toriel's robe, as well as a large collar with shoulder pads. He also wears a locket similar to the Heart Locket.

Final Form
Asriel's body becomes more geometric, his horns are longer, his claws get sharper and his teeth get sharper. He has a pair of wings that continuously change color, and his lower body becomes sharp and heart-shaped.

While this form is not directly named, it resembles the Delta Rune, which looks like the "Angel of Death" from the prophecy.

Personality
Before his death, Asriel was a docile, unadventurous, and loving child. He cared for the First Human as a sibling, and he trusted them when they came up with a plan to escape the Underground that involved the human consuming buttercups.

After Alphys resurrects Asriel without a SOUL as Flowey, he becomes incapable of feeling love. This makes him bored and resentful.

After temporarily regaining his compassion, he apologizes for his actions to Frisk and realizes the gravity of his actions as a flower.

Much like his father, Asgore, he commonly speaks southern U.S. slang.