Really not sure about Rain of Gore. First, it's totally reactionary. If our opponent has no lifegain effects, it does absolutely nothing. Second, if we're trying to win through general damage, this doesn't help a whole lot.
I would suggest Æther Flash, but it stabs you in the back pretty hard, and I'm not sure that switching out all your creatures with 2 or less toughness is worth it. I've always liked Defiler of Souls too, but it doesn't fit your deck in its current state.
Since Zurgo is never going to block, Bedlam might be worthwhile.
Deathtouch goes very nicely with Goblin Sharpshooter. Mark of Asylum makes fighting even more one-sided, but might not fit with the flavour you're going for.
I'd also cut Vindicate for Utter End once it's printed. Instant speed and exile instead of destroy are more than worth the one extra mana.
I'm not a big fan of Golgari Guildgate. I've found that, especially in a two-colour deck, it's usually preferable to have a basic land than one that enters tapped no matter what. I'm also not too sure about this life-gain angle when we don't have Sanguine Bond on the table.
Exhume might be on your cut list, since your opponents might have some nasty surprises in their graveyards that make it essentially a dead card. You could probably stand to lose Necrogenesis too, since a lot of your sacrifice outlets specify nontoken creatures.
A good card to combat graveyard hate is Repopulate.
The main thing that has me worried about this deck is getting attacked. One way to combat this is by running lots of enchantments (particularly ones that make Narset better at combat) and Sigil of the Empty Throne
I would suggest Æther Flash, but it stabs you in the back pretty hard, and I'm not sure that switching out all your creatures with 2 or less toughness is worth it. I've always liked Defiler of Souls too, but it doesn't fit your deck in its current state.
Since Zurgo is never going to block, Bedlam might be worthwhile.
I'd also cut Vindicate for Utter End once it's printed. Instant speed and exile instead of destroy are more than worth the one extra mana.
Not sure what to cut, though; your list is pretty solid. Maybe a land fetcher of Big Game Hunter.
Worldspine Wurm, Krosan Cloudscraper, Khalni Hydra, Liege of the Tangle, Panglacial Wurm would be good additions, just to name a few. The mana costs are pretty steep, so you'll want Elvish Piper and Quicksilver Amulet, and other creature-cheating tricks.
Not too excited for Time Stop, Sleep, Discombobulate or Khalni Heart Expedition.
If you're running Melira, you definitely want Cauldron of Souls.
Exhume might be on your cut list, since your opponents might have some nasty surprises in their graveyards that make it essentially a dead card. You could probably stand to lose Necrogenesis too, since a lot of your sacrifice outlets specify nontoken creatures.
A good card to combat graveyard hate is Repopulate.
Levitation
Indestructibility
True Conviction
Coastal Piracy
Also, your burn section is sorely lacking in heavy hitters like Cinder Storm and Mindblaze.