Going into F1 (death shroud) as necromancer during 75% and 25% will make you able to walk while everyone else is locked.
Exiting desert shroud (probably all shrouds) during 75% and 25% phasing, and the icicles AoEs from the sky attack is happening, you will eat all of the damage and go in downstate.
Going in downstate during the phasing because of the above makes the boss not respawn and locks everyone in combat.
Going downstate because of the above during the 25% phase and while the boss is on the side of the arena, he won't disappear and when players come back to the arena the boss will not attack ever again.
Dodging the icicles attack into someone's else AoE makes you get damage regardless.
Overhall the dodging of the attack above is wanky and doesn't always work correctly and you get damaged even if you get some evades.
During the launch up you can sometimes get instantly killed by fall damage even if you're full health.
In rare occasions, coming back from the 25% phase won't render the Whisper immediately and chains will fly all over damaging players (as seen in the clip in the tweet)
Again as seen in the clip, very rarely it will spam all skills without cooldown.
Sometimes the orb phase will start before he does the usual attacks chains (aoe knockback, phasing animation, tail attack, double half-arena aoe attack)