I like this deck, and based on our conversations the day of the event, I'd think about these small alterations if I was tuning my own version:
- Dropping the 4 Stonecoil Serpent, and adding more mana or interaction in those slots. The full suite of Deathrite Shaman seems very useful to me, for both triggering Vengevine as well as hardcasting stuff, should the game go a few turns, or as another tangential tool against Dredge and graveyard-centric decks.
- Anther option could be more off-color Moxen, to help more reliably power out the first turn Thalia or Collector Ouphe draw, which could help greatly when you know what deck you'e up against.
- 2-3 Lavinia would be another interesting choice, and could potentially be swapped in some of the floating slots. This would also keep the creature count up (for Vengevine triggering purposes).
- I think more graveyard hate is necessary in the sideboard against Dredge (likely the 4th Leyline of the Void, and maybe 1 more card).
How relevant was Thorn of Amethyst in your experience? It seems incredibly powerful in theory, but I'm wondering if you had time to cast it on curve, and if it proved worth the slot.