In Champions Online there are a ton of powers to choose from to outfit your hero the way you see fit. Two of the Mystic power sets are Sorcery and Supernatural and there are a few things you need to know about them.
Sorcery revolves around four different types of powers. A Circle of Power ability gives you big buffs while you stay within a circle. Circle of Summoning powers will summon a creature that will fight for you but you cannot leave the circle in which you summoned the creature.
Auras are buffs that buff your friends and Sigils are placed to hurt enemies around you. Invocation are the catch all spells that range from healing to other summons.
Because Sorcery contains four core types of powers each with multiple versions the set is getting quite large. Sorcery is actually becoming so extensive that it might be broken up into subsets like the Martial Arts line.
To clarify, Sorcery has Circles of Power, Circles of Summoning, Aura Sigils, and Invocations. Those are the types of powers but each has multiple versions. Apparently those versions are shamanistic, arcane, and necromancy. For example, you could have a Circle of Power for each; shaman, arcane, and necromancy, a Circle of Summoning for each as well and so on.
As for Supernatural,
Supernatural is a set intended to let you create a character that is supernaturally inspired: angelic, demonic, etc. Their powers are like, "Condemn your enemy with bolts of holy doom," "Infect your enemy with clouds of pestilent flies," "Bite your enemy and drain their living essence to yourself," and "Summon animals from the wilderness to serve your will." There's definitely a very wide variety of skills in this single power set. It is our intention to break this power set after launch into multiple sub sets. We have plans to add more to these sets in our ongoing post-launch power expansions.
There's more at the developer blog so check it out. While you're there register for the game!