I'd replace one of the Soul Warden effects with Guide of Souls, since it's got a better statline and gives you energy that can be turned into +1/+1 counters and flying. Sure it doesn't do any creature like they do but I think the tradeoff is worth it.

Ob Nixilis of the Black Oath is just bad. It's too much mana for not enough impact and there are just better things you could be doing. And Gonti's Machinations just doesn't do enough despite its low mana investment. I'd recommend cutting them both for more ramp, you've got a lot of 4 drops that you'd love to get out a turn earlier.

Peer into the Abyss should definitely be added in from the maybeboard. With your commander out you're going to gain a shit ton of life and kill multiple players. If you add more ramp like my earlier suggestion then it'll be a lot more feasible to hit that 7 mana number.

All that mass artifact hate combined with Ygra. It warms my cold, dead heart.

In total this deck seems split between a couple different things it wants to do. On one hand you have specter tribal with your commander, forcing a lot of discards. That's good but then you have a bunch of zombie synergy stuff with a tenuous connection to the first theme. and then on top of that you've got a third subtheme of dragons which seems very unlikely to actually come to fruition with it only having about 5 cards.

I think the deck needs some glue to hold it all together, and The Empty One just isn't that. He's all in on the Specter game plan with nothing to do with the Dragon or Zombie ones. Maybe cut one of the subthemes to lean heavier into the other two.

Dreadmalkin and Leech Gauntlet are both pretty mediocre. I'd recommend replacing them with more ramp (you have a lot of pricier cards here, including your commander. More 2-cost mana rocks would go a long way). I also don't think you have enough enchantments for Grim Guardian to be putting in the work.

Other suggestions would be Aclazotz, Deepest Betrayal  ^Flip (discard payoff), Hostile Investigator (Discard payoff and targeted discard), Sangromancer (Some lifegain) or Quest for the Nihil Stone (Cheap discard payoff). I do think you should be prioritizing adding more ramp first so you can get you specters out and start swinging faster.