Duke is usually a quiet and patient guy, he rarely loses his temper thanks in part to his upbeat attitude and goofiness. He likes eating pizza and meats, occasionally helping people, and sometimes hanging out with friends; but above those, enjoys staying to himself and sleeping. Duke dislikes a lot of noise, especially when they disturb his naps, he tries to avoid physical fights as he's more passive aggressive than people think; he also can't stand lengthy monologues, wearing sandals, and eating asparagus.
Due to a traumatic event he experienced as a child, Duke became an orphan and has since had amnesia. 2 years later, he was found by an adventurous, treasure hunting echidna named Hawk. Duke was trained in martial arts as a means of self defense, as Hawk with his wife, Kat-Rina, raised him. Duke has remarkable strength, speed, durability and power; all of which are matched, if not surpassed, by his mild mannerism and extreme patience. At the age of 12 though, as he lost control of his chaos powers during training, his mother was kidnapped by a group of thugs. She's been missing for eight years. To prevent this outburst of raw power again, he wears two black inhibitor rings that keep this vast, untamed energy in check. His uncle Trenton, Trey for short, is the CEO of a major weapons company, but is suspected of secretly being one of the most powerful crime lords on Mobius. Duke's heliokinesis is a powerful force on its own, and the medallion he wears inhibits his mysteriously obtained inner demon. This keeps it from bursting out in the middle of battle, allowing Duke to keep control over his actions and fight more efficiently. Not much is known about this beast, but certain legends have a funny way of connecting fiction to fact.
He can generate, manipulate, and absorb the various aspects of a sun; such as fire, heat, light, energy, radiation and gravity. Duke can fly, project energy blasts and constructs, and increase his physical abilities with this power. He can continuously absorb power from any star, the rate of increase will speed up when he gets closer and slow down the farther he gets; also he can manually increase the intake of solar energy himself, but this takes focus.
During combat, when Duke is without his medallion, he unintentionally unleashes his inner demon's power; this results in him becoming half demon with wings, claws, fangs, and a longer, sharp tail, a state referred to as Demon Duke. In this form he loses heliokinesis and gains lunakinesis, hallucikinesis, shape-shifting, and umbrakinesis, he is 100 times more powerful than base, and his chaos powers use negative chaos energy. He gains extra power during the night and even more when the moon is present, depending on the stage of the moon itself. His claws are sharpened shadows enabling him to cut through even the toughest of metals as though they weren't there; despite that most demons(in this series) are vulnerable to sunlight, he is immune to its effects thanks to his Lunar Scales. He is also immune to poisons, hypnosis, magic, and intense temperatures. He possesses techniques and other abilities in this form too.
Duke has an abundant supply of chaos energy thanks to his connection to the Chaos Force; with it he can augment his abilities, control matter and energy, and manipulate space-time. These abilities increase with added chaos energy, either from an emerald, Tikal's Chant, or when he removes his inhibitor rings. He has so much chaos energy its said to rival Shadow's, he can use this power for a few techniques. Using the seven Chaos Emeralds, he can go super.
Duke possesses high levels of strength, speed, durability, stamina, etc. He can lift large aircraft and strike with enough force to cause quakes and make fissures; he is so fast, he can move faster than lightning; he's tough enough to have 100 tons worth of rubble fall on him and get back up and he's completely immune to fire and heat. His stamina is virtually limitless when he's constantly exposed to sunlight. As are his other stats.
Duke has 15 years of combat training under his belt; he is well versed in armed and unarmed combat, favoring hand-to-hand combat the most. He can quickly understand and effectively learn many fighting styles like boxing, muay thai, and aikido. He can use these fighting styles in tandem with his chaos and solar powers to increase their effectiveness.
Now for the category that you actually want to know. Though he seems unstoppable, he's far from it; he has flaws just as the next person would. More powerful and experienced opponents can overpower and out smart him. Fighters with Lunar powers might be able to render his solar powers ineffective. Other chaos energy users can counter his chaos powers. If medallion stays off for too long, he'll begin to lose self control; acting more and more like a mindless monster. Though he can absorb a limitless amount of solar energy, there's always a limited amount he has at a given time. Overexertion of any activity will exhaust him like it would anyone else.