MTG Salvation

Hello!
I've decided to return to MTG EDH after a hiatus and would like to use Grimgrin as my commander! Grimgrin is my favorite legendary, and before I temporarily left EDH I played him extensively.

I would like to update the decklist from a more casual, zombie tribal deck to a no-holds-barred competitive deck. I don't mind completely revamping the decklist, or changing the play style (combo, aggro, etc), and money is not a problem for deck building.

So please, let me know what you think can be done to make this deck a reality, and what I should be looking for to make it!
Thank you very much for all of your help!

There are some Necrotic Ooze combos that work with Grimgrin. For example, Bloodline Keeper + Grimgrin in the grave = infinite power.

I usually see him enabling a zombie tribal deck.
If you don't want Zombie tribal, then I guess my first instinct is to abuse the fact that he is a free sac outlet. Constantly having access to a free sac outlet makes Grave Pact and Dictate of Erebos better.

You can maybe make a combo with Mikaeus, the Unhallowed.

It could be a kind of value attrition deck that wins with giant Grimgrin or combo.

Gravecrawler+Rooftop Storm+Grimgrin, Corpseborn=infinite sized Grimgrin.

Rooftop Storm+sedraxis alchemist+ Brain Freeze or Tendrils of Agony + any blue permanent = infinite sized storm

Rooftop Storm+Gravecrawler+ another zombie in play + phyrexian altar + bitter ordeal

Mikaeus, the Unhallowed is a nice combo card, with right kind of creatures around you can use your Grimgrin, Corpse-Born as sac outleft and pump him infinitely. The kind of creatures you are looking for is those you can easily get rid of the counters after undying have triggered, like Triskelion that also alone with Mikaeus can shoot everyone to death, Crystalline Crawler that also works as a mana rock or any creature with persist as you can decide if that creature will die with a persist trigger or a undying trigger.

Diregraf Captain zombie buff and opponent loses life if zombies dies
Havengul Lich cast from grave
Sidisi, Undead Vizier and Corpse Harvester as tutors
Vengeful Pharaoh nasty surprise
Fatestitcher non sacrifice way to untap grimgrin

Urborg, Tomb of Yawgmoth + Cabal Coffers combo gives loads of black mana, add Filth which you can sac to the grave and your creatures become unblockable.
Wonder can work too as to avoid blockers, or just a Rogue's Passage for your grimgrin