Asmodeus is a large, vibrantly-colored, and burly demon of intimidating stature. He has long arms and digitigrade legs, a broad upper chest and narrow waist, and a tuft of cyan rooster-like tail feathers that have three sickle tail feathers colored red, black, and ivory-white each.

His head is colored dark blue with red and white head feathers sticking out from a tuft on his head, and he has large feathers running to his chest. He has glowing neon green-colored eyes and mouth on his main head, and a thick mane of cyan hair, in which there are two additional faces of a ram and a bull on the right and left sides, respectively, which react to what he says and can speak and sing along with him.

In "Oops", it is shown that his body is a lighter shade than his head and he has light blue nipples that are heart-shaped. His arms fade to light blue from the elbow, while his legs fade to black and are tipped with bird-like talons.

Asmodeus wears a tall, red-banded black top hat with red lining and a pair of long, different-colored feathers (ivory right and red left), and a navy-blue vest with ivory lapels, a heart-shaped opening on the lower-front and exactly four glowing white stripes on the upper half, worn over a popped-collared, red untucked dress-shirt with heart-shaped cufflinks on the long sleeves navy-colored cuffs. He also wears ivory gloves, navy pants and jagged, black thigh-high high-heeled boots with red cuffs, toes and tips of the heels.

Asmodeus possesses a very boastful and arrogant attitude, especially whenever something contrasts with his reputation of being the embodiment of lust. Otherwise, Asmodeus values consensual lust, stating how it's about pleasure for everyone involved.

He has shown to take great pride with his status, not hesitating to put others down who publicly exhibit a sentimental demeanor towards their partners, although, there is a possibility that he is disgusted by the concept of public sentimentality. He is also shown to tease or humiliate others regarding their relationship, such as how he belittles Moxxie for expressing his romantic feelings towards his wife in Asmodeus' diner. Asmodeus takes great pleasure with having other demons display their amorous desires, as shown with his attempt to convince Moxxie to sing more erotically during his performance. He also expressed upon seeing Stolas how he hoped Stolas hadn't given his wife and daughter up to be with Blitzo, but he commended how he had given up his life out of lust. However, this was eventually shown to be very hypocritical.