Blizzard has updated their initial Mythic+ Affixes in The War Within blue post to clarify that while Fortified and Tyrannical initially alternate, both will become active in +10 and higher keystones.
I’ve updated the OP:
- Keystone levels +2 through +11 have the following affixes:
+2 Xal’atath’s Bargain affixes appear on a weekly rotation. - +4 Fortified or Tyrannical is active, alternating on a
weekly rotation. - +7 Challenger’s Peril is active on all keystones.
- +10 Tyrannical or Fortified is active, alternating on a
weekly rotation. - +10 Tyrannical and Fortified are active.
The one that was not active at +4 that week becomes active at +10.
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