First off, work in progress and I am not a modern player, so I have no idea if this is would be good in the modern metagame. I just saw that Thrasta + Grief from MH2 seem to work really well together, grief being a 0 mana discard effect that can remove any counterspells or killspells that may threaten Thrasta while also lowering its cost by 3. It means I have to play black if I'm going for the combo-aggro Thrasta on turn 2 idea and cast grief, but thats not too bad with cards like Slaughter Pact, Street Wraith, Memory Leak, and The Cauldron of Eternity, all of which but the last you'll only occasionally actually use black mana for.
For the deck itself, its cast Thrasta turn 2 or Summoner's pact it turn 3 or whenever you have the mana, play 4 0 mana spells, and hit them hard. If they kill Thrasta, do it again naturally or use cauldron of Eternity to bring it back, or somehow finish it with your durdley other creatures. Protect the combo with Grief and/or Memory Leak.
For the sideboard, Utopia Sprawl is nice if you need additional help ramping into Thrasta, Cauldron of Eternity, or Carnage Tyrant. Carnage Tyrant is for shutdown control decks, hopefully it plus Castle Garenbrig can help you win. Slitherhead is a early small creature to help against aggro and makes Thrasta a bit stronger. Gutshot is for extra protection, especially against deathtouch kind of decks, and I also included more Cauldrons incase you needed them.
For the maybeboard, I'm not sure about living end, as I don't have a way to free to cheat it out, such as with cascade or Sram's Expertise. Ghoultree is weird since I'll be putting creatures in my graveyard anyways, but I don't think its fast enough and doesn't have trample. Same Idea with Ghalta, but I just don't have much power. Surgical extraction and Apostle's blessing are good ways of protecting Thrasta, but I wasn't sure if it was useful enough or really needed.
