A very well focus chapter, Hiro kept the whole focus on the fight, not something Hiro does that often.
Is Invel trying to recruit Gray to his ranks, it seems that is what he is trying to do. We see Devil Slaying magic has its drawbacks, it for shadows that we are going to have Gray vs Natsu one of these days, and now it gives Gray an excuse for fighting, he can't help it he has gone insane, if what Invel says is true, but Gray has proven everyone wrong he can control this power so far.
Brandish taking Natsu, Lucy, and Happy, not clear is it an antagonist move, is it to protect them, either way unintentionally protects them because Invel was about to spell the beans about E.N.D., best Natsu get out of there, it is clear Brandish is a conflicted character, she doesn't know what to do anymore, maybe she just wants to talk to them, and hear their side of their story before she decides are they enemies or not.
What Invel did when he trap Gray and Juvia forcing them to kill each other, dirty move, and not original, this is similar to Merody sensory link and what she tried to do to those two and herself, which makes Invel look more like a coward, at least Merody was willing to risk her own life, Invel is just going to make them fight.
In the end, this could finally Gruvia canon. I bet that could happen, so thank you Invel.