Grave Pact and Sheoldred, Whispering One create more outlets to have your opponents to sacrifice. Also cards with proliferate like Contagion Clasp , Contagion Engine , Inexorable Tide , Spread the Sickness , and Viral Drake .

@MiniDragon, I should have updated my maybe board, but Grave Pact and Sheoldred, Whispering One are on my list of cards to order. As far as proliferate goes, it is an interesting mechanic, but I think i'll be going in a different direction. Thanks, though!

Mindwrack Liege would be nice for some boosting and creature-cheating. Also, I'd suggest any of the Eldrazi creatures with Anihilator.

@lil_cheez, I don't have the funds for more eldrazi creatures.

If you want to sac some creatures, you are going to need a Grave Pact ! Nothing says sac 'em like the pact!

Tribute to Hunger is a good replacement for Thunderheads . I feel like it's a stronger play since you drop a creature of theirs and you get some HP to buffer you a bit. Thunderheads just feels like a stall tactic to me and you can do better.

Innocent Blood is cheap and easy and it hits the whole board.

You are running ideal colors for Cruel Ultimatum ! That's always a saccing-card advantage-booya-moment!

I'd also suggest some sweepers just in case. Decree of Pain is an excellent choice. Life's Finale is also good.

I run the same colors in my Bolas, Like a Boss! deck. You can check it out for ideas. It has a sub-theme of creature saccing as well.

start by adding your commander... you have 101 cards

if you want to go tribal zombie you need to go all out... kinda seems like your deck is half zombie and half vampire haha. pick a theme and stick with it. that'll give you plenty of card slots too. also where are Demonic Tutor and Terminate ?!

here's my deck, maybe you'll get some ideas? Thrax the Assassin. if you feel inclined to leave some feedback or upvote while you're there that'd be awesome

The idea of your deck is very similar to mine: sacrifice and kill your opponents. Some cards I recommend are Ashnod's Altar , Phyrexian Altar , and Bitterblossom . I agree with outofnothing0, you need to focus on one theme. The creatures are all over the place and most do not belong with your goal/focus. Curse of Death's Hold is irrelevant in commander, so put in Attrition or something. Not enough zombies to make use of Endless Ranks of the Dead . If you want ideas, you can use my deck for ideas: He Who Paints Your Butt Red.

Lastly, you have 100 cards in your deck, and Thraximundar isn't in the list, so you need to cut one card.

Not enough tutors. Liliana Vess , Demonic Tutor , Corpse Harvester are all really great things that go with the them of the deck. Ashnod's Altar is like the best sac outlet that has ever been made. Things I don't like for the deck Niv-Mizzet, the Firemind just seems like a good stuff addition as does Platinum Angel . Dimir Keyrune just doesn't do it for me tbh. Volrath's Curse just doesn't do it for me either. Also I would look into how many of your lands come into play tapped. It would suck if you had to wait on turn 7 to be able to play thrax. I would look at Urborg Volcano , Tresserhorn Sinks , Salt Marsh , Jwar Isle Refuge , Frost Marsh , Akoum Refuge , and all the Guildgates. Things like Urborg, Tomb of Yawgmoth , Cascade Bluffs and Sunken Ruins and some more basics would honestly go a lot farther in fixing your mana base and they wont come into play tapped. Let me know what you think of these suggestions!

I would replace Moan of the Unhallowed with Clone or Phyrexian Metamorph . I'd rather have another Rune-Scarred Demon or Platinum Angel then 2 zombies anyday. Also Undead Warchief Grave Titan . Also Hell's Caretaker might be a free sacrifice mechanic. If you would like help picking cards to remove I'd be glad to post again. Let me know what you think. +1 and thanks for the upvote!

Capsize and Desertion are powerful blue cards you could add.

Chrysis, thanks for the suggestions, I'll consider them.

Thassa, God of the Sea Unblockable General, Hero's Downfall Solid Removal Blasting Station + Rooftop Storm + Thraximundar = Game wins Damnation (or Decree of Pain if tight budget) Snapcaster Mage Vampiric Tutor Temple of the False God Ancient Tomb Lazav, Dimir Mastermind Traumatize Jace, Memory Adept