Arioch is an evil entity that serves as lieutenant for the Lord of Chaos, Shuma-Gorath. Arioch is extraordinarily powerful, as he is made of infinite energy and able to make himself as strong as he wishes to be - therefore his strength is only limited by his imagination. He makes his initial and only appearance in Marvel when he confronts Dr. Strange, who is on his way to Shuma-Gorath's dimension.
Strange Tales #13
Doctor Strange and his temporary mentor of black magic, Kaluu, travel to Shuma-Gorath's home dimension 1,000 planes of existence away from their reality. As they reach the 998th plane of existence, Kaluu collapses and begins dying due to the strength of the realms energy. Strange, having absorbed enough black magic by this point so as to exceed even the late Ancient One in power, is able to continue on the journey without being affected by the realm's energy. As Strange leaves behind his dying tutor of black magic, Kaluu, he enters the next dimensional plane, just one plane away from Shuma-Gorath itself and pulsating with an even stronger energy than the last one.
The demon Arioch appears and after a brief exchange of words the two begin to battle. Arioch uses his power to summon a spike that appears to impale Doctor Strange, though the Doctor uses a spell to create a body double and tackles Arioch from behind. Arioch scoffs at Doctor Strange's attempt to try and fight him, stating, "You fool! You can't fight me! I am as strong as I wish to be -- as strong as I can imagine! You cannot stand against that power!" Arioch then proceeds to mutilate Dr. Strange's face with an energy blast and brags that he is an omnipotent entity.
Doctor Strange admits that he cannot stand up to such great power possessed by Arioch. However, Strange also states that he does not need to stand up to that power when he can take it for himself. Strange proceeds to use the power of the Wings of Needless Sorrow to absorb Arioch's essence and merge with him, thus defeating the demon. Later, after Doctor Strange defeats Shuma-Gorath, he releases all of the energy he had gained from the chaos demon as well as Arioch. Because Arioch's energy was freed, he may possibly be in his dimension waiting for the right time to attack again.
Powers and Abilities
Arioch is an immensely powerful chaos demon whose power is only limited by his imagination - therefore, his strength is incalcuably high. During his fight with Doctor Strange, Arioch demonstrated powers such as levitation, reality warping, and energy projection that causes rot and decay. Arioch's own words show him to be a nigh-omnipotent entity. Arioch's power is such that the master of black magic, Kaluu, was unable to even approach his realm before his body started to die from the realm's energy. Arioch's power was able to give Doctor Strange the needed boost in magical energy that would allow him a fighting chance against Shuma-Gorath.
Arioch's appearance revealed that he had no true weaknesses to speak of. However, he was unable to prevent Dr.Strange's magic from absorbing his very essence.