Echo of Varshan Shield - how does it actually work?

I’am wondering how does Varshans Shield work, specifically.

He seems to get shield when he goes in middle for the “dance” sequence and when alts appear. However once in a while he seems to just random get it.

It is just a bit boring and weird - and makes it take 3-4 times the amount of time Lord Zir takes.

he gets it form the adds, each one he sucks he gets a different ability.

actually he gets his shield when he attacks with the tentacle. if it hits you besides blinding you he gains the shield