1. Completing a Mythic+ dungeon will reward mainly Mythic Power, more info in Loot & Times section;
2. Mythic+ dungeons have different difficulty levels: a level 3 dungeon will be more difficult than a level 2, but easier than a level 5. There is no cap of available Mythic+ dungeon levels. However, greater levels will have an outstanding mechanics and so, the difficulty increases rapidly.
3. Enemies in the dungeons will deal more damage and will have a higher health pools with each level your party conquers.
4. A higher-level Mythic+ dungeon rewards better loot, more info in Loot & Times section.
How-to steps on Mythic+ dungeons can be found by visiting our forums at https://sunwell.pl/mythic