This is a fringe as hell cedh mono-black combo deck that wins by assembling an infinite loop and killing the table on turn 3-4. It's been a work in progress for a couple years now and I've sunk way more money and time into it than it deserves. It's as optimized as Balthor the Defiled will ever be.
Winning
Make infinite mana.
Then infinitely cast and activate Balthor, using one of the win cons below.
Now, I know what you're thinking. "Both of those mana engines are 3 card combos that your commander doesn't contribute to. It's not gonna get there". But... Ad Nauseam.
As the best draw spell in the format, you practically win on the spot if you can resolve Ad Nauseam. Well that's the case when you're in colors with access to stack interaction at least but it's still good here...
Game plan
The most common line to your early game is ramp, tutor for Ad Naus, draw until you're in single digits and use the ramp to power out / tutor for / discard your creatures and activate Balthor for the pieces to an infinite mana loop and go from there.
If you already have most of the pieces to a mana engine, you don't need to rely on Ad Naus at all, but Ad Naus is definitely plan A. If it gets countered (or if you see them in your opening hand) fall back to Ad Naus #2 Necrologia or Ad Naus #3 Necropotence.
Necrologia is a bit of a balls-to-the-wall card, as you pay the life whether it resolves or not. However, it's stupidly strong if you can stick it. Draw 30+ cards, dump basically everything but the best ramp, any artifact pieces of the infinite mana combo you chose to pursue, and a tutor if needed. The following turn use that ramp to reanimate all your goons with Balthor and you should be able to win from there.
Necropotence can make some lines difficult since you can't discard through it, but it's still Necropotence.
If you can stick a Chains of Mephistopheles, Oppression, Mindslicer or Contamination, good. But I generally don't tutor towards it as it doesn't really advance our own game plan.
Mulligans can be pretty difficult here as you're looking for both ramp and a big draw effect (or tutor), and Balthor really doesn't do anything early game. So mulligan aggressively. Bricking does not feel good. That being said I've fishbowled this about 150 times and I'd say turn 3 wins are about 35% and turn 4 50%, which seems pretty damn consistent to me. In real games when I get stopped, I'm usually able to recover pretty quickly to threaten a win again the following turn.
What's the point of Balthor?
The million dollar question. Because he looks like Gimli and he's the fucking man.
In all seriousness, the deck would be significantly stronger with Sidisi as the commander, but significantly less fun - for me at least. I like playing an obscure general at a cedh level. He has a cool splashy effect and he drives the build of the deck into unfamiliar territory. He's often the combo turn enabler, reanimating a core mana engine piece or tutor creature like Sidisi alongside a bunch of mana dweebs that pay us back the majority of the mana we spent to use him. He's a weird roundabout infinite mana outlet, netting us infinite reanimations of all our black creatures. He's not actually very good - which I mean as a compliment, as it adds a whole swimming-upstream dimension to piloting the deck that takes a shitload of skill. No one will ever groan when you play him in a competitive pod, since they can't in their right minds say he's overpowered and you're clearly here to have a laugh and try something new. There's a tonne of variance to every game with him and he never gets boring. And he's Gimli.
Buried alive piles
Apart from finding the remaining pieces to the main wombo-cazombos mentioned above, the best pile I’ve come up with is...
Razaketh, the Foulblooded + Pawn of Ulamog + Priest of Gix. This wins the game with 6 life and 0 mana after reanimating them with Balthor: Priest enters, 3 floating. Sac it to Raz to get Phyrexian Altar, pawn generates a token. Sac the token to Raz to get Nether Traitor. Play Altar off the 3 floating. Sac Raz and the token pawn makes to the altar for 2 floating, play Nether. Make infinite mana with the Nether Traitor combo, play and activate Balthor again, sac something to Razaketh to get a win con.
Feel free to make suggestions. There's been heaps of single card discussion in this thread if you're interested - https://www.reddit.com/r/CompetitiveEDH/comments/9wmh31/deckhelp_lets_make_balthor_fruit_loops_competitive/ . And check out the change log as I've kept track of all the changes since I started trying to get this to cedh standards.