more ramp for mono black:

Dark Ritual

Cabal Ritual

Sol Ring

Jet Medallion

Temple of the False God

Thanks Undead_Assassin, don't forget to +1 if you like the deck!

I've had fun with Chainer, Dementia Master in the past and Nightmare Incursion/Bitter Ordeal are both excellent cards. Also, Temporal Extortion is a mono-[B] deck's best way of forcing a win.

Black Market is a MUST for any mono- edh.

With only 18 cards to build from, I don't feel like all my suggestions will be as helpful as they could be, but I'm no stranger to mono-black commander, so here's what I'd suggest:
For mana ramp: Doubling Cube, Deserted Temple, Thespian's Stage, Sword of Feast and Famine, and even Explorer's Scope (if this deck is somewhat aggro) are decent options. I also run Lake of the Dead.
Strata Scythe is a third option for land-based pumps, but you'll probably want to include a Urborg, Tomb of Yawgmoth if you run too many non-basics.
I don't know how strong you want to play the infect angle, but you should also run creatures with wither, Blowfly Infestation + Corrosive Mentor + Crumbling Ashes is brutal.
I'd also include Sheoldred, Whispering One, Midnight Banshee, Grave Pact, Black Sun's Zenith, Nettlevine Blight, Corrupt, Corpse Cur, Hand of the Praetors, Dauthi Embrace and Virulent Wound.
Other than black staple cards Sign in Blood, tutors, creature killers and recursion effects, Pestilence seems like a good inclusion also, what with all your ramp and everything.

Thanks all! I will update the list here, you gave me a lot of ideas! Undead_Assassin, JA14732, WicKid52 and themlsna please come back after to see my update!

Check out my deck for mono ideas Sheoldred queen of Urborg, Demonic Tutor is a must Hatred is on my to get list for my deck

Check out my Mono black edh here. It's based on Anowon, the Ruin Sage.

I think this is a fantastic deck! I would only pull the Batterskull and maybe put in a Sword or the Jitte if you want equipment. I'd also say Homeward Path maybe. The other one that I'd consider adding is Rogue's Passage, you know some unblockability ensures a one turn kill with Skith :)> Great deck mang! Had I seent this before I built mine, I'd probably start with this because it's a better base then what I started with and is keeper for sure!

Thakns a lot DReyRose, I will look forward to your suggestions!

I wouldn't run Lake of the Dead without Crucible of Worlds. The acceleration is great but you'll really be feeling it the longer the game drags. Plus, if you add the Crucible, you can add Strands of Night, which is one of the best reanimators in mono-black EDH. It can also let you recur Cabal Coffers if someone blows it up.

Scrying Sheets is a must if you're running snow-lands.

Burnished Hart and Myriad Landscape are some of the best non-green ramp around.

Another thing to keep in mind is that black cannot deal with artifacts or enchantments. All Is Dust and Nevinyrral's Disk can take care of that problem (as well as Karn, which you've already got).

Another suggestion is more protection for Skithiryx: Lightning Greaves and Swiftfoot Boots are all good options for that.

Hope that helps!

Thanks for the feedback Ruffigan, so you would suggest me to put in Crucible of Worlds? What are the things I should remove for it and tis little package? What are the weakest cards in here?

The list looks very fun now, I do like it a lot. I've been looking for a really cool mono black list for EDH and this is it.

I would suggest Dictate of Erebos and Grave Pact (which was already suggested). Since you'll be playing a lot of threats, your creatures will often be the target of removal. These cards punish your opponent for doing so.

And seriously, you can't go wrong with Pack Rat with all the card draw and mana ramp you have. That card is insane.

Also, Temporal Extortion is hilarious.

Thanks a lot Undead_Assassin, what you say makes me happy! I am looking at your suggestions and will update the deck soon!

I would remove World Slayer. Even though you've got some evasion it hurts you just as much as everyone else. Desecration Demon is also not too great in EDH.

Another suggestion is Expedition Map. As they say, if you're playing mono-black, Cabal Coffers is your commander, and this tutors for it (or Wasteland, Urborg, Tomb of Yawgmoth, Volrath's Stronghold).

Ok, so I am going to remove Worldslayer at the profit of an expedition map. Desecration Demon was here because it is a cheap CMC creature, would you have other suggestions Ruffigan?

Ok Jdvanliew, what would you suggest as a fun name? Sorry if I offensed you...

You could replace Doom Blade with Tragic Slip. It requires a creature to die to use effectively but it can hit black creatures and also gets around indestructible. You could also replace Silence the Believers with Ashes to Ashes or Mutilate.

Thanks Ruffigan, I will apply those changes in a minute or so!

Name: 'Ware the Black Death, or, Beware, the Black Plague Cometh.

I second the recommendation for Strata Scythe. I use it in my own deck and it's reliable, or it baits out the artifact kill and leaves a clear space for either of the lashes.

Grafted Exoskeleton might be a nice bit of equipment for your not infectors as well.

Vesuva, because multiple copies of Cabal Coffers is awesome. MAOR MANAS.

Beseech the Queen is a nice additional tutor. It is a bit of a mana check though, but early game it allows you to grab things like Phyrexian Arena which will give you a nice hand advantage, or later game will allow you to fetch fatties. Less flexible that demonic or vampiric, but I still find it very useful in any of the decks I have that run black.

Night's Whisper, an addition to Sign in Blood.

Mikaeus, the Unhallowed without his best friend Triskelion? It is an infinite combo, and I know some people dislike them, but I thought I'd bring it to your attention anyways.

Inkmoth Nexus

Unspeakable Symbol and Eldrazi Conscription because lets beef up those creatures more.

That should be enough for now

Wow Evee142, thanks a lot for all those suggestions! I will put them in the maybeboard for now until I find what to remove for them. I will surely include a lot of them, and Triskelion is the forst I will try to fit in.

@thegigibeast

No problem! I also run a Skithiryx EDH deck, and it's my favorite. Spent several years tinkering with it, so it's fairly consistent, at least in my meta. (When people agree to play against it. Usually they see Skittles and just refuse to play against infect D:)

Have a look at mine if you wish, maybe you'll see more than what I suggested that might fit in yours :)

Cards I suggest:

.

Terrain Generator

Korlash, Heir to Blackblade

Squelching Leeches

Phyrexian Altar

Nightmare

.

Achievements I suggest:

.

Wombo Combo!: Kill 2 opponents in one turn.

Infinite Damage: Deal infinite damage with Mikaeus, the Unhallowed, a sac outlet, and Triskelion.

Overcoming a Weakness: Win a game against a Melira, Sylvok Outcast deck.