Does anyone know about the raid boss's attack named "March of the Decamator"?

I play on mobile with auto mode on and trying to beat hard mode.

There's this attack that I haven't seen in any videos or in the boss's list of skills or attacks where it floats for a bit (maybe the time where I meant input the QTE but it doesn't appear) and points its sword downward then it stabs the ground with it(sometimes the QTE appears only for a split second before it hits the ground) and insta-kills my team.

It usually happens when it reaches 20 million hp but in my latest attempt only few minutes ago it triggered on 60 million hp.

My question is this: Is this attack avoidable somehow? If it is, then how do I avoid it's condition?

Because I wasted SIX attempts on this (and all due respect to devsis) BS.