Your curve is way too high, especially for a Grixis-Stays deck. I'd suggest smoothing out some of the higher stuff into lower costs, like trading
Dread Cacodemon for something along the lines of a
Fleshbag Marauder,
Mortician Beetle or
Malakir Cullblade,
Altac Bloodseeker,
Deathgreeter,
Blood Artist, or a Gatekeeper of Makakir. If you really want a laugh,
Goblin Sharpshooter could be ridiculous enough to almost work in your favor. It almost looks like this deck was built around
It That Betrays, so I'd suggest getting your hands on one. I didn't see a
Grave Betrayal, you might be interested in that. It really looks like you're working in favor of a late-game deck, so you definitely need
Harvester of Souls. The card draw will give you a
relentless assault of big baddies late game. And just as a last card recommendation, throw in a
Nightscape Familiar.
On a final note,
Grimoire of the Dead. 'Nuff said.
I do have a
Grave Betrayal, a
Nightscape Familiar, and an
It That Betrays if you feel they'd work well in the deck.