Altar of Dementia could potentially find a home here.

If you need dudes in the bin you can suicide mill or even mill out an opponent in a long grindy game.

I am always a huge fan of sacrifice outlets so YMMV. Spawning Pit is my favorite sac outlet and can get nasty with Dictate of Erebos effects if you are feeling particularly dirty.

The Amonkhet Lilliana's comes to mind

If you want to stray from zombie tribal Grey Merchant of Asphodel is really sweet, especially with how much black you've got going on.

Exsanguinate and Sanguine Bond might work too

Dolphin_Jesus Thanks for the suggestion! You weren't the only one to suggest Altar of Dementia so I added it to the list.

Aaerys I thought about including cards that cause my opponents to lose life but for now I didn't want to because I wasn't sure if that could ruin the fun of my friends. Just being able to get a bunch of Zombies seems like it would be more fun. Good cards tho, thanks for suggesting them!