Wilhelt, the Rotcleaver EDH Deck Tech
Introduced in the Midnight Hunt commander decks, Wilhelt is a zombie tribal commander that offers a lot of benefits. The ability to generate a 2/2 black zombie (albeit with Decayed) when another Zombie dies is nice, and being able to sacrifice a Zombie during your end step to draw a card is icing on the cake. My version of the deck focused on tokens with cards that give buffs to Zombie tokens and anthem effects. You can find the deck list on Moxfield.
Cemetery Reaper, Death Baron, Lord of the Accursed, Narfi, Betrayer King, and Tomb Tyrant each give other Zombies +1/+1 along with other benefits. Eternal Skylord, Gleaming Overseer, and Vizier of the Scorpion collectively give your Zombie tokens Flying, Hexproof, Menace, and Deathtouch.
On the subject of tokens, Cleaver Skaab is great in this deck. By sacrificing a Zombie, you create 2 copies of the sacrificed creatures. This could also create the 2/2 black Zombie with Decayed as well. Champion of the Perished is another threat, as the number of tokens the deck generates giving it +1/+1 counters constantly. Undead Alchemist is a double-edged sword. It can potentially create a lot of tokens, but some decks would love to have extra cards in their graveyard. I think the risk is usually worth the reward, and offering an alternate win condition is good too.
Of the other permanents, artifacts are basic Dimir mana rocks. Necroduality and Rooftop Storm are the very powerful, able to create blowouts if left unchecked. Coastal Piracy can let you draw a ton of cards, as your creatures are potentially unblockable against many decks. Oubliette is a great way to deal with a troublesome creature or commander.
If you can afford to cast it, Army of the Damned is a great way to generate extra tokens. Distant Melody can draw tons of cards to the point it may be dangerous to use late in the game. Aetherspouts is strictly worse than Cyclonic Rift, but is still a potent defensive card, as you simply can’t block much. Sudden Spoiling can be used offensively or defensively, although I much prefer it on attack.
When upgrading, the first place to look is of course the mana base. Cyclonic Rift should replace Aetherspouts or otherwise find a place in the deck. Other Liliana planeswalkers could help the deck as well. Beyond that, your personal preferences and the local meta will determine what else needs changed, if anything.