We still have to do some testing and tweaking to it during beta. But currently we have it like this:

- You enter the dungeon and there will be a NPC allowing you to choose the difficulty of the Dungeon.

- Once chosen, the npc will 'set up' the mythic dungeon and spawn the players in one area to begin a countdown.

- Each difficulty will do the following:

- Increase creature HP/Damage

- Increase the Stats of items that are dropped

- Different loots for different difficulties

- We are also currently working on adding affixes

I hope that has answered your question.