After the sandstorms are created, the boss will periodically do an earthquake move as indicated below.
Unless you have 100% Earthquake Immunity, you will be shocked for 10 seconds.
After a short while of doing the earthquake, the boss will do a one shot move.
You can time the one shot move by counting the number of moves the boss does.
The boss usually does it after 3 moves used.
If the move animation takes a long time, ex. rolls, it will do it after 2 moves used.
To avoid the one shot, you must stand in the sandstorm to get 3 stacks and get petrified to become invincible.
Players can prep 1 or 2 stacks of the debuff to make sure you get 3 stacks in time.
The invincibility effect still lasts for a bit after wearing off.
In RU, the one shot mechanic, doesn't one shot anymore.