I really want to put in some ways to make sure my creatures have 1 or 0 power when they die (I currently have 6 creatures that don't fit Shirei's requirement -- Crypt Ghast, Grim Haruspex, Midnight Reaper, Pawn of Ulamog, Phyrexian Plaguelord, and Sifter of Skulls). I was thinking at first that I should do -1/-1 effects like Phyrexian Plaguelord, but there aren't really enough that make the cut beyond that one. After that I found Sorceress Queen, which seemed promising, but again, there aren't very many effects like her. Any suggestions?

Any opinions on Overeager Apprentice?

I like Bog Witch over the Apprentice. Overeager Apprentice has better synergies but is more useless if your commander is out of action.

With the number of creatures you have, Oversold Cemetery can help as a back up. You could also put your commander in the graveyard after a board wipe and grab him back first. Though, it is a bit of a pricey card.

Gift of Doom might be a good way to protect your commander.

I would recommend cutting a couple creatures for a few more pieces of removal. A board wipe preferentially but you are lite on removal overall. Pestilence could be useful here. Acts as a mass sac outlet for a B or a board wipe for a little more.

Those are good suggestions, I've been trying to find ways to make Shirei indestructible so I will definitely add Gift of Doom. The point about being too focused on the commander is very valid, I've definitely noticed that when she gets removed I stop completely. I really like Overeager Apprentice, but I might add Bog Witch as well for backup ramp. I will add Oversold Cemetery to the maybeboard and get it if I feel I need it.

RiotRunner789 do you have any ideas for removal? I'm not sure on removal that's cheap $-wise that is actually playable. Its not like I'll put a Doom Blade in here.

Tragic Slip is a great budget removal and with the amount that stuff should be dying, should kill almost anything.

Drag to the Underworld should be a kill any creature for a BB.

Then their is also Terror. Simple and effective.

As far as board-wipe removal there is Nightmare Unmaking, Mutilate, and Dead of Winter. Though Dead of Winter isn't quite budget since you would need to change to all snow-covered swamps.

I'm surprised I don't already have Mutilate in the deck!

I also own several Tragic Slip and at least one Nightmare Unmaking, so I'll add those to the list. Drag to the Underworld is a good idea.

I'm going to thin out the maybeboard today. Is there anything on it that seems like it really needs to be in the main list?

First, I'm going to point out things that may not be the best on the maybeboard,

Blasting Station: Semi-repeatable but free sack outlets are just better. Unless you can continuously flicker something from the grave to the battlefield this should be cut.

Netherborn Altar: Highly situational. Better off just having protection for your commander or ramp.

Diabolic Intent: Personally not a fan of tutors but this is on theme and can help you in a pinch. My philosophy is to only tutor for a response and not for the win but to each their own.

Nim Deathmantle: 4 is a high cost to hold up to sometimes save your commander. Better protection available.

Panharmonicon: You have 8 creatures currently with ETBs which is a bit low to include this.

Universal Solvent: Mono-color decks have weaknesses. Typically in EDH certain board threats can be handled by others at the table. I would cut it unless your meta has little to no interaction for threats.

Witch's Oven: Love this card, just not for EDH.

On second thought, your maybe board is REALLY big. I'm just going to go with what cards stand out.

Augur of Skulls, Burglar Rat: Black's best advantage is denying your opponents advantage. Burglar rats is the better of the two since it will cause your opponents to discard 3 cards. Augur is only better if there is that One player in the meta that needs to discard.

Orzhov Enforcer: Helps to build a token board presence. Best case scenario this trades with something and you get a token and you repeat this every turn.

Sling-Gang Lieutenant: Same as above but better. Helps with some life-gain and gives you blockers/sac fodder.

Thorn of the Black Rose: Are you low on card draw? Yes, then add it. You should be wide enough to keep monarch. Good on draw? Then give it a pass.

Yawgmoth, Thran Physician: You typically don't want creatures with power greater than 1 but... This is card draw, removal, and a sac outlet. If you have it then use it.

Dredge the Mire: Seen this been played. 4 mana for three creatures is just good. Those creatures may not synergize well but you should at least get one good threat and it should help to have one big dumb creature.

Mutilate: Just a good board wipe. Sometimes you need to hit restart. If you have the funds, Dead of Winter is strictly better but needs snow-swamps.

Altar of Dementia: Two mana on a sac outlet that is harder to remove than a creature. Yes, please.

Meekstone: This will defend you from a ton. May also draw some hate but can save your from the R/G trample guy.

Smokestack: Really good in your deck. But, if you play it, be able to win in the next few turns and have some kind of recursion or the mana to replay your commander. This is a salty card, so be aware of your play group.

Grave Pact: With this and a sac outlet you should be able to own the board. This is a hard yes.

Oversold Cemetery: Could act as a good backup plan for your commander dying too much. Send him to the grave then re-play him. Then grab your graveyard recursion creatures next and your back fairly quickly from a board wipe without needing to draw into it.

Phyrexian Arena: Steady card advantage. One of my favorite cards.

Deadly Rollick: Free removal. Your running a linchpin deck (as in your commander is essential to be on the field) therefore this card pulls more weight cause if its dead your probably dead.

Imp's Mischief: Just a fun card no one expects in mono-black.

Cabal Coffers, Cabal Stronghold, Nykthos, Shrine to Nyx: If you own them you should run them. Also, especially if you have more than one of these, cards like Torment of Hailfire, Black Market, In Garruk's Wake, and Exsanguinate should be looked at more closely.

Hope that helps.

In order:

My thing about Blasting Station is the situation where you go into your end step with Shirei, return a bunch of creatures, and immediately use all the triggers from Blasting Station to sacrifice them for next turn.

I actually just added Thorn of the Black Rose because it essentially means no one else will ever have monarch: if anyone else ever gets it, your trigger goes on top to take it back, resolves first, and you steal it back. Makes monarch slightly less appealing when the guy you got it from will constantly take it back without having to do anything for it.

I will definitely add Burglar Rat, it is very good card advantage. The reason I don't like Augur is because it only hits one player and only your upkeep. Might add Black Cat to draw less hate?

I want to add Yawgmoth, but am afraid to get it and be disappointed my his performance. I will try it out, but I might leave him on a wishlist.

Sling-Gang and Enforcer are great cards, especially the latter having deathtouch. However, for whatever reason, my group doesn't really care about me until I start getting tokens. Better to sit in the shadows.

Added Mutilate.

Want Grave Pact, currently outside my price range. Will add later.

Oversold Cemetery, same thing as Pact and Yawgmoth.

Arena, great card. Should probably get it.

Deadly Rollick is outside price range as well currently, hopefully the hype will go down a little.

Lands: definitely outside the realm of possibility, those are happy happy dreamland.

Imp's Mischief is so cool.

Thanks for the feedback, that definitely helps.