Superhuman Physicality: As a demon & devil Issei is much stronger, faster, and tougher than most humans.
Body manipulation: Sebastian is shown to be able to twist someone's arm just by twirling his finger
Mind manipulation: Demons are able to trick the minds of people into perceiving things or persons which are not there.
Hellblaze:This technique generates black flames which has the ability to nullify healing capabilities and regeneration.
Levitation: It is shown that, when the first time Sebastian encountered Ciel, his feet weren't touching the ground.
Enhanced senses: Sebastian is able to find humans based on smell-including ones he has never personally met-, is able to deduce if they are dead, alive, or injured and be able to discern if someone is a human or a member of another race.
Transformation: Sebastian has demonstrated that he can switch between his human form to his true demon form and back quickly. Furthermore, it is implied that Sebastian can change his appearance at will, be it humans or creatures. He can also shapeshift his own body to weapons.
Manipulation: Beyond making contracts for a human's soul, Sebastian has offered to make other deals or attempted to charm and manipulate people in order to get what he wants. William has called this the "signature" ability of a demon, and states that it works by "deceiving prey with sweet words and dragging them into darkness."
Soul sensing: Demons can pick up signs of life by sensing the souls at long-range.
Immortality: Demons can live forever, and they can heal/regenerate from any injuries, even if their entire bodies are destroyed.
Manifestation: Sebastian can create objects and weapons.
