Mythic+ Dungeons are a new type of challenging content especially tailored for the groups of five players. Originally introduced in Legion they offer players a scaling end-game challenge and while similar to the common 5-player dungeon runs, Mythic+ dungeons come with a timer that players need to beat, reminiscent of the Mists of Pandaria and Warlords of Draenor challenge mode. They also feature additional mandatory objectives for players to accomplish during the run, emphasizing not only speed but also performance.
To successfully complete the Mythic+ Dungeon run, the players have to defeat all bosses within the dungeon as well as clear a fixed amount of trash packs before the M+ timer runs out.
To begin the Mythic+ dungeon run, you will need a special item - a Mythic Keystone. Each player may have only one Mythic Keystone at a time, and will only receive one keystone per week.
There are 3 ways players can get a mythic keystone.
Firstly, it can be obtained as a reward from the last boss of any common Mythic 0 dungeon. Secondly, players can also receive it as a reward after completing any other M+ run, upon which, the keystone will be located in the rewards chest at the end of the dungeon. Lastly, the mythic keystone can be obtained as a reward from the weekly Great Vault for completing the m+ run during the previous week (more info regarding mythic+ dungeons rewards below).
Mythic+ Dungeons also have levels that increase the difficulty of the dungeon (enemies deal more damage and have higher health pools with each mythic+ level) and improve the rewards: the higher mythic+ dungeon level keystone you complete, the higher item level loot you get as a reward.
In addition, Mythic+ dungeons gain special effects called affixes at certain levels which add even more complexity to the M+ run. These affixes add additional mechanics for players to play through on both trash mobs and bosses.