I don’t want to discredit you, but I’m curious. How long ago was it that you were seeing every Cassyva player running Nether Summoning? Personally, I have not reached S-rank (nor do I care to) but I watch nearly 3 games for every 1 that I play. I haven’t seen Nether Summoning played more than twice on all of those games, iirc.
In my own personal usage, I’ve had no success with it. However, I only ran it in a joke deck, so I don’t blame the card on that one. For what it’s worth, I’m not saying it’s a bad card. Rather it is frequently unreliable.
Arcane devourer, I still believe it’s spot in the deck would be better dedicated to other cards.
Lightbender, I still believe is a good card. I was not saying it shouldn’t be run, I was simply pointing out its interaction with Death Knell (being a 3/3 body), nothing more.