In either case, you can jump over the shock wave to avoid taking damage.
The last mechanic that appears throughout the fight is that of shards of ice crashing to the ground.
85%
When the legendary hawk sentry reaches 85% of his health bar, he incorporates new mechanics into his combat repertoire. It will form an AoE which extends in a semicircle in front of it. When its arm hits the ground, it repels the players and inflicts great damage to those affected. In the process, a snow trap will form around it which sucks the players, without inflicting damage to them.

75%
At 75% of reached life, a new attack is added to the combat. The sentinel will target a player and cause an AoE to appear under his feet. When the AoE is filled, an ice crystal crashes, inflicting damage and icing the affected players.

50%
The boss transforms when he has only half his life. It will not be possible to select it during its animation. You can then see that his body is changing, more precisely he loses one of his arms. Take care to avoid the explosion and the debris of ice, they repel you. Take advantage of this short moment of respite to get back on your feet. Several new mechanics will take place in combat.Two mounds of ice will form on the ground, on either side of the sentry, and release countless scoops of ice in three directions.You can only climb on the mounds when these scoops of ice disappear.

Please note: the sentry will try to destroy one of the mounds. It will focus and momentarily stop attacking you while an AoE forms on one of the mounds. Be sure not to find yourself on the one she's targeting. The mechanics consist in that all the players find themselves standing on the mound which is not aimed, in order to have enough height to jump over the shock wave which will result from its attack.
At the same time from half of its life, the sentinel forms a new AoE which extends in a semicircle. This attack devastates the area of an ice sheet when the sentry sweeps the ground with his arm instead of making you spin. This attack occurs quite often and is an improved version of the simple punch.

25%
From 25% of the sentinel's life, three mounds will appear. And from 10% of his life, four mounds will appear.