Mythic Plus changes in patch 7.2.5

These are future plans for Mythic plus dungeons that will first be tested on PTR to see the outcome.

Completing the run on time will have the same results it currently does in 7.2: you’ll get a new Keystone for a random dungeon that’s 1-3 levels higher than the one you just completed, based on how quickly you finished.
If you complete the dungeon but don’t make the timer, you’ll get a Keystone for a random dungeon that’s 1 level lower than the one you just used.
If you don’t complete the dungeon at all, you’ll have a Keystone for the same dungeon that’s one level lower than the one you just used.

You no longer receive additional chests at the end of a run for completing it quickly.
When you finish a Mythic+ dungeon, the chest at the end will contain two items and an appropriate amount of Artifact Power.
If you beat the timer, regardless of how quickly, there will be a third item in the chest.
Keystones can still upgrade by 2 or 3 steps, so you can quickly get to a difficulty level appropriate for you.

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