Are you sure Black Sun's Zenith is better than Dimir Machinations? Many of your best cards cost 3, so you can transmute for card advantage (Necropotence), interaction (Fleshbag Marauder, Hero's Downfall, Toxic Deluge), or a synergystic card (Ashnod's Altar, Buried Alive, Necromancy). Both BSZ and transmuting Dimir Machinations are equally mana intensive, but the great flexibility provided by the transmute ability looks really powerful to me.

Emzed, that's an interesting point regarding having a ton of good cards at CMC 3 that I could transmute for. My problem with transmute in black (this doesn't apply to blue) is that black has multiple unconditional tutors. If I wanted another tutor in here, I'd probably go for Demonic Tutor or Entomb since they can fetch me any card. I've purposely kept my amount of tutors down. Really appreciate the suggestion though!

I do agree that Black Sun's Zenith isn't the greatest boardwipe. Sometimes it can be mana-intensive to kill everything you need to. I may take it out and put Murder back in. The deck is short on instant-speed removal.

I noticed you have Merciless Executioner but not Fleshbag Marauder. Not a fan of the art? lol

Head Collector, I found I didn't really need both. So yes...when I cut one I decided based on art haha