Vassago is a lanky avian demon who greatly resembles a Scarlet macaw, with red feathers, a white face, and a hooked black beak. He also has rather long, gold-tipped purple feathers on the back of his head with a gold-colored streak through the center, and red eyes with no irises or pupils, which are often covered by a pair of yellow visor-shades that vaguely resemble a star or crown. Vassago wears a red suit-jacket with a gold-trimmed popped-collar, black lapels, a star brooch, a giant "X" and a small star design on the back, and rather long, extravagant tails that are trimmed with black, the top part being purple while the bottom is a gradient of two shades of orange. Over this, he wears a white dress-shirt with two black buttons on the center. Vassago's clothing also features black pants and white arm-length gloves and thigh-high high-heeled boots - his gloves having black torn-like cuffs and two red stripes in the front, while his boots have black toes and tips of the heels, as well as an "X" shape on the bottom center. Immortality - As demonic royalty, Vassago is a biologically immortal, being able to live for a long period of time and only able to be killed by angelic weaponry. Platform creation - Vassago can conjure a levitating star-shaped platform for himself to ride around on. He is seemingly capable of producing smaller star-shaped platforms for himself and others to walk on, as shown in "Crimson Sky". Pyrokinesis - Vassago is capable of summoning and manipulating fire or generating explosions, as he shows Stolas in their flashback, generating a spell that then covers him in soot and forces him to remove his shirt, or summoning a fire spell that explodes the boat he and Stolas were using in "Crimson Sky". Evocation of Lights - Vassago is able to evoke light, to generate lights and make them create images, which he does when Stolas evokes a spell to make them see the Moon (that of the Earth), and where Vassago evokes a crowd of small purple lights which form an image of Stolas and himself dancing together. Skillset Bilingualism - Vassago was raised speaking both English and Spanish. Vassago is shown to be a high-strung and mindful demon within Hell's royal hierarchy, though unlike most of the aristocratic elite, he holds the responsibilities of Hell's governance in high regard. As such, he expressed a distaste for unfairness and harm, especially when the matter of another Goetia such as Stolas was involved. This was shown during Blitzo's trial when he noted Stolas' absence and advocated that he needed to be brought in, then being genuinely disturbed when Andrealphus accused Blitzo of being responsible for the assassination attempt on Stolas. Similarly, he expressed annoyance toward Andrealphus' condescending attitude and his attempts to win the case against Stolas going so far as to call Andrealphus an arrogant idiot for his comments. However, he can also be patient, charming, clever and somewhat manipulative. When Stolas was confronted by Stella during the auctioning of his items, Vassago calmly stated that Stolas was there as his guest, and went on to charm Stella into letting him stay. Additionally, when Blitzo was caught stealing the locket, Vassago hastily placed himself between the imp and Andrealphus, claiming that Blitzo was his valet to get him out of trouble. Vassago has a tendency to slip between English and Spanish in conversations, although he seems to slip into the latter more at times of high emotion. He also seems to have a whimsical taste for music, as he cheered for Stolas presenting his defense in song.

He is a lanky, peacock-like avian demon with a short light blue beak, and cyan eyes that both lack pupils and irises and have periwinkle upper-eyelids. His feathers appear to be mostly white with slicked-back, short, light periwinkle hair with a few dark blue spots. Inside his beak, his tongue is a cyan color. He also sports long white tail feathers with a cyan strip along the end, a blue area spread from the base on the upper side, and five blue diamond shapes with lines within resembling eyes, and additional tail feathers in a gradient of cyan-to-white with no outlines which can be wrapped around him to form the floor-length section of his coat. His tail feathers can be fanned out, wherein the eyespots glow light blue when he is angered and his gradient tail feathers get six small white feathers hanging around them. He wears an extravagant coat that is mostly shades of light blue with white details. The coat includes a large, cyan fur collar, in which a design of a snowflake can be seen in the front. He also tends to keep his arms hidden away in the fur of his coat. Under his coat, he wears a long-sleeved navy-blue shirt with a white-trimmed high collar and four white buttons, white pants, and long navy-blue over-the-knee heeled boots. He accessorizes with a cyan snowflake-like crown, and a pair of long white opera gloves.

Stella is a tall avian Goetic demon with a short pink beak and small, gray face-markings below her eyes. Her eyes have red-pink sclera, white pupils, and long feathery-like eyelashes, and she wears pink eyeshadow. Her feathers are white, and she has long, gray-tipped, white feathery hair with a large gray stripe on her head. She also has black, claw-like nails.