Great deck! I do have some suggestions but I am not a pro at commander so take everything I say with a grain of salt.

I think that Magus of the Coffers could go really well on here because he is essentially a Cabal Coffers on legs. If you find yourself needing some more ramp this could be a great card.

I always like to put Skirsdag High Priest into any black deck due to the number of tokens it can generate. However he is a human so he Mikaeus, the Unhallowed cannot resurrect him.

I always put a Myriad Landscape into my commander decks due to the fantastic ramp it provides

One thing I noticed while looking at your deck was that Disciple of Griselbrand is a human so he can't be resurrected via Mikaeus, the Unhallowed. This isn't a huge thing and he can still be in the deck.

Expedition Map can be used to tutor for your Cabal Coffers early game for some early game ramp.

Arcane Lighthouse is a bit situational but it is super useful if you run into hexproof commanders like Lazav, Dimir Mastermind or Uril, the Miststalker.

Darksteel Plate may be good to provide Mikaeus some protection if you find that he is being picked off a lot.

Volrath's Stronghold is a great card to bring back combo pieces or just good creatures.

You might need a bit more card draw in this deck in order to get it to run smoothly, but I haven't played with it so you would know better.

Lastly, your curve looks a bit odd to me, but this might just be because I play aggro.

One last thing I forgot to mention was that if you need more comments on this the EDH sub-reddit (https://www.reddit.com/r/edh) is a great place to get more feedback if you haven't already posted it there.

Thank you for your time Bricksolr and comments!

I will consider Magus of the Coffers and Volrath's Stronghold for sure. Added them to the maybe board for now as I need to make room for them.

For now the curve is not a problem, same for the draw but i haven't played the deck enough often so I might have to review those points.

Again, thank you!

The main things you want to run if you're avoiding infinite combos is just stuff that gives you a ton of value. Lots of ETB/LTB effects. You seem to be on to this with stuff like Rune-Scarred Demon. Also, try to find as many ways as possible to capitalize on the lifegain. You'll still die to ten poison or 21 commander damage, but black has a ton of ways to spend life for big value. You have Necropotence, why not Phyrexian Arena?

I agree that your curve needs work. Look into mana rocks if you want more ramp. Worn Powerstone, Thran Dynamo, Hedron Archive, Dreamstone Hedron, etc.

And as a Lazav player; yes, Arcane Lighthouse is something anyone with a hexproof commander really does not not want to see across the table.

Also... Attrition.

Oh that reminds me Stronghold Assassin is pretty much a mini Attrition but it also comes with a body and it is a zombie.

After playing several games, I found out that the lifegain mechanic is not working in EDH. Bleh. Thank for the advices I will see what I can do! I run Thran Dynamo in my Triplets deck and I ppretty much like it, seems like I will try this card in this one too.

nice looking build

here some cards to consider:

Cauldron of Souls is a very powerful card with mikaeus

Mournwhelk is pretty nasty

Vulturous Aven, Merciless Executioner/Fleshbag Marauder has great synergie with mikaeus and or Grave Pact

Oh! Looks like Cauldron of Souls might be an interesting guest. I'll keep that card in mind for sure :D