Grimgrin, zombies can't be cEDH?! Help me shun the nonbelievers!

[TheGreatR]

Grimgrin, Corpse-Born was the first mythic rare I ever pulled, in the first box I ever bought. Lore-wise, he's a chad compared to the virgin Wilhelt, the Rotcleaver. And for that, he is my go to commander!
He has his main combo with Gravecrawler and Rooftop Storm, and being in black and blue makes tutoring and countering perfect for trying to get the combo off.
Does anyone have any suggestions to make this decklist better? Even if I have to give up some of the "zombie-ness" of the deck so that it is a reliable Grimgrin combo engine, I'd like to stop losing so consistently to cEDH decks at my LGS. As much as I love a zombie hoard, it seems it's better to go big and fast with one or two creatures, than to go wide.
Happy to answer any questions too! A lot of zombie staples aren't in here because I took them out due to being too slow...

https://deckstats.net/decks/133173/2659542-ub-zombie-edh-updated

[Morganator 2.0]

I'd like to stop losing so consistently to cEDH decks at my LGS.

Describe these decks to me. Do they consistently try to win around turn 4? As a non-believer I have little hope that Grimgrin will be on par with actual cEDH decks, but if these are just high-powered instead, we might be able to do something.

[Athreos]

The nonbelievers shall be shunned indeed. I have a similar list here (it's not cEDH yet, but I'm working on it) but I use Wilhelt as a commander.

https://deckstats.net/decks/77815/2245782-it-s-alive-

In my deck I am going to add some counters, like An Offer You Can't Refuse, Delay, Swan Song, Wash Away. In your decklist, I would replace Dissipate with one of them. You can also add more counters replacing Bad Moon, Whip Of Erebos, Shadows of the Past and Empty the Laboratory.

Then I'll add more combo pieces. If they manage to exile your Gravecrawler, you'll need something to combo anyway. I play Liliana, Untouched by Death because she can make every zombie in your deck a potential Gravecrawler. You can also play Altar of Dementia and Blasting Station for alternative win conditions with the same combo.

Diabolic Intent is a powerful and cheap tutor in a zombie deck. I tried using Corpse Harvester many times, but I don't recommend it in cEDH because of his high mana value and because is not gonna tutor you anything until your next turn, and usually he's gonna die before he can tutor anything at all.

Last thing, Skullclamp is going to make you draw soooo many cards in this deck...I strongly suggest you add it in your decklist.

[TheGreatR]

@Morganator
In the pod I played last week, I was swept by blue green Tatyova, Benthic Druid ramp that took 4 turns in a row before even playing Nexus of Fate, and blue white Urza, Lord High Artificer, I couldn't even tell you how I lost because it happened so fast, Aetherflux Reservoir hit the board, they proceeded to pick up their whole deck and the rest of the pod conceded it was a victory.
And yes, turn 4 and the table was told "Do you have a response? No? Ok let's go next!"
I know it's foolish to think a 5 cmc commander in the colors with peculiar ramp options is going to be "cEDH" but I'm also fine with being "high-powered" too!

[TheGreatR]

@Athreos
I agree with replacing Shadows of the Past and Empty the Laboratory, but Bad Moon saved me from Humility! I feel like Dissipate is good enough against Nexus of Fate and similar combos to the one I'm playing myself. Would you recommend replacing them with more counterspells, or since they are my "card draw" replace them with more reliable card draw? And I know I'm playing black and I shouldn't care too much about my life total when I am drawing cards, but with Whip of Erebos is my safety net, do you recommend a better way to not die to self inflicted wounds (Witch's Clinic?) or do I man up, and go down to single digit life with a perfect hand?

Diabolic Intent in, Corpse Harvester out. Good call coach! Skullclamp was also on the way in too!

If you don't mind me asking a few questions about your deck:
Ive been considering these cards but I don't want to add them if they are duds. Would you say you get value out of:
Razorlash Transmogrant
Leyline of Anticipation
Cleaver Skaab
Compelling Deterrence
Change of Plans
Military Intelligence

Thank you so much for you help!

[Athreos]

Fair enough to keep Dissipate, exiling spells could be usefull sometimes. I find that usually spending less mana to counter a dangerous spell is more worth it, but of course that depends on your more frequent match-ups!

I play with black mana decks the most of my time, and I can tell you this: life is a resource, don't be afraid to use it. Especially in cEDH, you are going to face many combos that can kill you even if you got a lot of life. If you can pay life to get card advantage, board advantage or tutors, just go for it. Most of the times, the amount of life you paid to get these advantages is less relevant then the threat of the opponent.

About the cards you mentioned:
- Razorlash Transmogrant is a recurrent card draw with my Wilhelt. Against not-monocolored decks, I can pay 2 black mana each turn to get a card and a decayed zombie. Since against monocolor is quite weaker, I understand if you don't wanna add it to your list! But you could use it to easily untap your Grimgrin each turn most of the times, if you couldn't manage to play Gravecrawler yet.
- Leyline of Anticipation is sooo great. In a creature-based deck as ours, having the chance to cast them at the end of the opponent's turn (or actually when you need it the most) is life changing. In cEDH, having flash in all of your cards means you can play your combo pieces at the optimal timing, reducing the risks of removals and counters and gaining a heck of a lot of control in the game. I play it in almost every blue deck I have, and often I'm happy to play it even if I have to cast it paying all her 4 manas.
- Cleaver Skaab is not optimal. I keep him because he can easily make useless most of the single-target removals of my opponents by activating his ability when the removal spell declared the target. The problem is he usually doesn't survive the turn I play him.
- Compelling Deterrence is in my deck because I don't have yet Cyclonic Rift. Just keep going with that one 
- Change of Plans can defend some of my combo pieces while making me draw cards, feeding my graveyard and powering up my creatures. Not bad for an instant, but of course it requires some mana if you wanna protect more creatures.
- Military Intelligence is going out soon. It was an ok card in casual commander, but in cEDH it's just weak. I'm replacing it with Necropotence! I hate having to exile the cards I discard, but drawing that amount of cards at will it's just overwhelming.

[fire5167]

Hmmm, well most BU cEDH decks can function without casting their commander a single time, so in theory it shouldnt matter who the commander is (that much). So I guess im technically a believer.

With that being said, in my experience, cEDH decks are the easiest to build top-down rather than bottom-up. So maybe start with a 85ish BU shell and then throw in like 15 zombie flavor cards?

You have already started with the deck building, so I would maybe pick your favorite 10-15 zombie cards and replace the rest with staples. Im talking Mana Vault, Mana Crypt, Necropotence, Opposition Agent, FoW, FoN, Swan Song, Flusterstorm, Thoricle, Demonic Consultation, Reanimate, Notion Thief, Narset, ancient tomb, urzas saga, walking ballista, snuff out. The list goes on If you dont play these cards its basically by definition, not cEDH-worthy. also Im assuming you dont have a budget as cEDH generally implies there is no budget. Moxfield is a great tool for making cEDH shells.

Other than that, I love the creativity. I know the cEDH restrictions often stifle creativity unfortunately, but I like the effort!

[TheGreatR]

@fire5167
I added just about all of what you recommended except for the cards that pass the $100 mark and personally like Withering Boon over Snuff Out. cEDH is budgetless but I am not so fortunate. If there's any recommendations from here, let me know. Thank you so much.