Steg is a tall and muscular fusion with four arms, light skin, and long brown hair which at the top resembles a pompadour. His Gemstone is in his navel in the middle of eight pack abs.
He wears Steven's shirt, now torn open at the chest and shoulders, and Greg's shorts. He also wears Steven's sandals.
Personality
Although most of his personality is unknown, his mannerisms imply that he is smooth, optimistic, and almost titillating.
Abilities
As a hybrid fusion, the reach of Steg's abilities are unknown. However, he does showcase many unique powers, amplifying those of his components, and clear physical strength and agility.
Natural Abilities
Superhuman Agility: Steg is shown to be an agile performer, spinning Pearl in the air and dancing with skill.
Skillset
Musical Proficiency: Following Steven and Greg's steps, Steg is shown to be a musical talent, a rockstar. He is shown to possess a pitch-perfect voice and the ability to play his "weapon," a double-neck electric guitar, alongside Opal.
Inherited Powers
Speed of Descent Regulation: As he is about to unfuse, Steg slowly descends from the air, in a similar fashion to Steven.
Unique Abilities
Levitation: Steg seems to have the ability to levitate himself and others with music. Perhaps this is a mix of Steven's magical high-jump and Greg's power to reach people through performing.
Steg's name was confirmed by captions of the episode and credits on Apple TV.
Steg's voice actor, Ted Leo, is in a band called The Both with Opal's voice actress, Aimee Mann, which seems to be the inspiration for Steg and Opal's duet in the movie.
Steg is the first fusion to be 100% male.
Steg's pompadour might be a reference to "Steven and the Stevens" where Steven One had his hair in a similar style.
The pompadour is also a trope of masculinity in anime, showing that Steg is a fully male fusion.