Hey man I really love this build. Definitely a +1 from me!

I feel like your deck is very fine tuned. I love it. The only recommendation I have is more card draw:

Forgotten Creation , Graveborn Muse , Kindred Discovery , Vanquisher's Banner , Mystic Remora , Windfall , Whispering Madness , Read the Bones , and Phyrexian Arena to just name a few!

Also with ramp, I'd recommend Wayfarer's Bauble , Gilded Lotus , and Heraldic Banner .

I hope all this helps! Love the build.

Another SUPER FUN card I forgot to mention is Cryptic Gateway . It combos really well with Intruder Alarm .

Tap 2 zombies, put one into play, untap all of them and do it again!

Pair this combo with Kindred Discovery and you'll be drawing and casting zombies like crazy!

Pair these with your commanders Scry/Drain ability and you'll be able to make a really big impact on the board.

These suggestions are more for fun and an interesting idea. The previous comment is much more important.

I never knew about Kindred Discovery . But I feel like I have almost too much card draw as of right now, especially once I throw in Kindred Discovery . Regardless though, that's definitely getting added.

Also I'm surprised I forgot Gilded Lotus exists. I use it in like every EDH deck I own.

Lastly I'll be replacing Pillar of Origins with Heraldic Banner because that's just a no brainer.

And btw I actually took out Vanquisher's Banner and Phyrexian Arena from the original deck plan and replaced them with Door of Destinies and The Immortal Sun respectively. I figured that The Immortal Sun was overall better than Phyrexian Arena since I can ramp to it fairly easily, it reduces the cost of everything I cast and buffs my creatures while shutting down all planeswalkers and giving me card advantage every upkeep. It was just too good to pass up. Same thing with Door of Destinies . The fact that this deck swarms zombies so fast would give that card an absurd amount of counters and make my board state explode.

Thanks though! If you have any more recommendations I'd love to hear them.