There are two major changes in the Mythic Difficulty version of this encounter, one in each phase.
During the Ground Operations phase, Iron Reaver will repeatedly scatter Volatile Firebombs throughout the encounter area.
These Volatile Firebombs react identically to the Volatile Firebombs encountered during the air phase on Normal/Heroic difficulty
Iron Reaver casts Firebomb three times during the grounded phase - right at the start of the phase, between the second and third Barrage, and just before the final Blitz
Because the health of the Volatile Firebombs is low, players do not need to save cooldowns to kill them, or use legendary ring effects
Assigning specific ranged DPS to kill the Volatile Firebombs in designated sectors of the room will help ensure the mechanic is handled smoothly
During the Air Operations phase, when Iron Reaver casts Firebomb, she will summon four different types of Firebombs, rather than just the Volatile Firebombs from Normal/Heroic difficulties. The different types of Firebombs are indicated by colored light beams.
If any of these Firebombs are allowed to detonate, the raid will take Fire damage and gain a stacking Firebomb Vulnerability debuff. Each type of Firebomb has a different-length fuse and must be handled in a particular manner.