1x Soul Conduit: Funny and bad but also useful.
I'm a fan of Marchesa and wanted a multiplayer deck that features her. What I came up with is a midrange creature-oriented deck.
*Painlands help me stay behind my opponents in life so I can consistently get Dethrone triggers.
*Unleash critters want to attack anyway and can be recurred with Marchesa out.
*Hellhole Flailer can go balls to the wall and maybe get a kill, or if I want to hound someone, I can *situationally* use him to pick who is on the throne and single out one opponent.
*Cerberus and Chasm Skulker help me recover from a board wipe.
*Syyg and Looter help feed the Skulker.
*Looter is powerful when it has Dethrone.
*Scourge of the Throne, Garza Zol, and Thraximundar are threats/win-cons that synergize with Marchesa.
*Grixis Charm's Trumpet Blast synergizes with Skulker tokens. It can also bounce a blocker or pesky global enchantment/artifact, or kill a critter.
*Virulent Swipe makes my opponent think twice about blocking. It's really good with Splatter Thug. Rebound is built-in card advantage.
Criticism is welcome. I want to buy singles and build this, so getting some feedback before I spend money would be appreciated.
23 lands and no ramp feels weak to me. Were I playing this deck I'd have 4x Fellwar Stone no questions asked and in place of Shivan Reef and Underground River I'd run 4x Izzet Boilerworks and at least 2x Dimir Aqueduct and take the free 2-for-1s that would help me hit 5-6 mana for my bomby finishers. I understand what you're saying about lifeloss + Deathrone but this is multiplayer. You're one person playing a deck with no lifegain; odds are you'll be able reliably trigger DT for most of the game and so I don't see any big incentive to ping yourself. For cuts I think that Virulent Swipe is weak and I'd also shave the Bloodfray Giants. I'm not in-love with Grixis Charm either.
Cauldron of Souls + Unleash/Deaththrone is a decent combo. Just so everyone's on the same page -1/-1 and +1/+1 counters cancel each other out so Cauldron + Hellhole Flailer means infinite blockers/nukes/etc. You get the idea. I'd probably play 2 of those over the Charms, remaining Bloodfray Giants or any of the fat other than Scourge of the Throne.
Not blockers, unfortunately, because unleash. Could block for cheap with Butcher Ghoul, but it's not as big.
Unleash only prevents blocking insofar as the critter has a +1/+1 counter on it. If you Cauldron of Souls back a Hellhole Flailer and choose to Unleash it the counters will nullify each other and it'll return to play with no counters as a 3/2 and still be able to block. I played against this exact deck a lot since one my friends thought that it was super busted lol.