Necron... they seems to have been chosen as the eldar nemesis wich is nice. I could play with a necron ally at some point and i saw there power first hand that's something scary. If i was asked what would you bring vs necron i would have 2 main answers. 1 the crimson death formation as you suggested, against the list you were facing it would not have done much but well at least there i think i would field one of those (might be because i love flyer^^). And the other things would be spyder a real load of warp spyder. Like two squad of eight or something like this >< might be a bit over kill. But they have speed, incredible speed so to speak, vs some foot necron it should do the job and even against there vehicule, the light transport thing, does not have enought armor to resist a spyder barrage of shot.And as a bonus you wound on initiative wich if i recall isn't were necron excel.
I would probably concider a guardian ost and a autarch, with support of one wraithknight, one aspect formation of spyder and reaper for saturation shot (maybe some hawk too for obj grabing), some dire avenger shrine in there aswell. The crimson death formation, and may be an avatar in bonus for the fun of it and the fearless aura. Can annoy some of his unit in cc i think. Well that's all theoricaly with an eldar only list and i'm not sure i can field so many things within 1850 points.
The bikes are nice, I like the pose for the hand, make for some high speed high five^^
I guess the shadow isn't finished yet but so far i'm not into it. With the mask of a different color, same for the blade, and some further detailing it will surely look great. But for now there is way to much gold to my liking. The model is great though. It's still a wip so i should change my final words for later
Cheers