Add control on Phase 2 of Mythic Fyrakk has been very important and the top guilds have their raiders take the Engineering Profession to use a BFA Engineering enchant to help!
Belt Enchant: Personal Space Amplifier is an Belt Engineering Enchant back from the Battle for Azeroth expansion.
Engineers can use equip this enchant to their belt and once every 10 minutes, can knockback enemies that are close to them. This has been used in Mythic+ extensively in Mythic+ since BFA to knock mobs into melee, move mobs out of Sanguine and more, but it hasn't really been used much in raid until now.
So why are Liquid and Echo using Belt Knocks? If you've done the fight on Normal or Heroic, you know that Fyrakk will Deep Breath across the arena and drop a very long line of adds. On Mythic difficulty:
All of these are great reasons why guilds want to group up the adds into one big clump. The problem is that some of the adds are VERY far away from the middle.
The adds cannot walk on their own even if killed and so knocks and grips are the only way to get the adds to move. While some classes have knocks as part of their utility kit, if players go Engineering, every raider can have a knock! If you plan on getting Cutting Edge this tier, you might consider going engineer.
This isn't the first time that Engineering in Mythic raiding has been a significant boon on progression. On Mythic Raszageth, the intermission knocked players to the side, dealing damage to the player. But players found out that the old