Warped Exarch:

Vigil:

Wait until you get to mission 6.

That Scarab has a mind of it's own and it will occasionaly just destroy all the cover, even if there are no units in it's vision.

You'd think it would stop firing after one shot, but it just keeps hammering away until it just vapourises you.

I think its supposed to do that.

Well yeah, its supposed to do that, as Forge say someting like that we got the stones to cover us, but not forever. something in that direction.