Necrium Blade is a card I don't see people talking about or playing at all... But I think this card is crazy strong. I've been playing a bit of tempo rogue since the expansion dropped almost entirely because curving out with the blade into egg into free 5/5 is an insane tempo play. Blightnozzle Crawler isn't quite as insane, but it is powerful, and since it's 4 mana it's a nice follow up turn to playing the blade. I also think that the blade has some juicy possibilities with Carnivorous Cube but I haven't been able to find a way to make it work yet.
Tried to play malygos rogue it has a solid win condition but if you don't draw malygos it can be frustrating to play.. will probably try the tempo approach to necrium blade too which deathrattles did you choose?