I will release an update for CP soon (most likely v1.3) which will contain a new game mode that offers you a new dungeon with a new challenge. Canonically it is a continuation of the storyline from the original game. How that is possible you ask? I will explain it. Keep in mind that this here contains spoilers!
After Leximus seals away Chaos and his body disintegrates so his soul can be united with Chaos once again, something unexpected happens. Because Chaos has already been weakened throughout the whole game, an external force disrupts these events and Leximus' soul is transported into a dimension beyond Chaos. He is not within one of the 4.3 billion universes created by Chaos but in different one, a new one. I will not spoil the story behind all of this, but there is new villian. Of course, Leximus' friends will be there as well. Because this universe is not a physical one, there are not the same limitations as in the universes created by Chaos (also because of the reason that all heroes have actually lost their physical bodies). Again, I will not go into details as not to spoil anything.
How do you get the "Beyond Epic" game mode? Simple. If you have beaten the game at least once in any mode (i.e. if you have unlocked any additional game mode so far), you will have "Beyond Epic" unlocked. In "Beyond Epic" you select a save slot that will be used as base for the game. The only prerequisite is that Sydon has already joined the party. You will start off with your current party, all your equipment, items, etc. and all the other stuff. You don't have to have level 100 with your party, but it is recommended as you get lots of goodies after defeating Hellvoid and defeating him with anything less than level 100 is a bitch. It's hard even with level 100.
"Beyond Epic" will offer one new big dungeon with an additional storyline, possibly several minibosses, new puzzles and a final boss that makes Hellvoid look like a kitten. It's even likely that you will be able to save your game whenever you want. Just be careful not to overwrite your old save file! Once you enter "Beyond Epic", you can't go back anymore!
What's so special about "Beyond Epic" and why is it even called "Beyond Epic"? Because the power of your party will tenfold. The maximum level will be 1000, your stats will go insanely high (which includes HP caps at 99999) and your damage capabilities will be beyond epic (expect normal attack damage in the 100000's to become frequent). Within short time your level should go over 400 (because the point is that you fight the last boss with a level around 700-800). Additionally to that each and every party member will obtain the ability to supercharge their power using Chaos. This will be beyond epic.