Do you think Gray Merchant of Asphodel would be good as a finisher? Or at least sideboard tech against burn?

I actually used to use Gary quite a bit in the SB and there was a bit of an issue with both resolving him (low curve and mana pool) as well as most of my stuff dying before he could come out. I need more testing against aggro but the Pharika's Cures and Eternal Thirst have been pretty good. I also usually bring in Master of the Feast since burn has a hard time dealing the 5 to him and I can usually race well with his help. Also, Phyrexian Revoker might become a 4th copy of cure or a second copy of thirst if it continues to seem not needed.

Some Boon of Erebos makes for good defensive measures against things like Drown in Sorrow and Back to Nature and some good offensive combat tricks.

Why caves and confluence?

Boon of Erebos is one card I've been considering. It would be nice against Drown in Sorrow, though the real problem this deck has is Anger of the Gods. I haven't put too much effort into looking, but I feel like there isn't too too much against that card besides just playing things like Master of the Feast.

PartyGoat, I decided to have a white splash for the Erase in the sideboard. Whip of Erebos is incredibly difficult to beat and it's nice to have a cheap spell to counteract that as well as some other key cards. I've been happy with it thus far.

Nice