it seemed like the droid not emitting the large purple circle was hitting people extremely hard. We just had to cross our fingers and hope it didn't decided to pick the same person twice in a row (which it did a few times). We weren't sure how the targeting worked, but it appeared random, and could be a huge headache if RNG doesn't want to be nice.
Completely avoidable - in hard mode that will one shot you so you are going to have to learn how to avoid it.
I'm not going to tell you how and spoil it - I'll let you guys figure it out on your own.