The Premise: Night of the Living Dead
The idea for this deck is to do what Zombies do: relentlessly overrun their prey. With Wayward Servant and Plague Belcher, you get them coming and going. Zombies entering the battlefield hurt your enemies. Zombies leaving the battlefield hurt your enemies. You can, like I have, get to the point between Diregraf Colossus and Plague Belcher that you have so many Zombies out, sweeping the board is a liability for your opponents—and that's when you do it yourself, destroying your foes in a kamikaze (zombikaze?) attack. You can also use Bontu's Last Reckoning on a turn where Song of Freyalise hits its final ability, making all your Zombies indestructible, vigilant tramplers for that turn.
Where the Deck Needs Help
I am not at all sure what to use in the sideboard and what the mainboard is missing. I feel like there's too little removal, but the exchange is more Zombies. With Death Baron out, you just keep churning out deathtouch Zombies who are fine trading recklessly into the opponents' creatures because it only helps out Plague Belcher and Diregraf Colossus. For recursion, I decided to give Gruesome Menagerie a try-out because I often end up in a situation where all three possible targets are in the graveyard, and Song of Freyalise tends to help a couple of turns with mana.
I feel that perhaps I am missing some hand disruption or more targeted removal in favor of just throwing out more bodies. If that's effective here I have no idea. I'd also like to have more card draw in there than I currently do, but space is rather limited. I could make room for, perhaps, Collected Company as a way to cheat out more Zombies quickly. Or maybe Heroic Intervention to save my Zombies from a board sweep or spare the Belcher from a smartly-targeted removal?
Plague Belcher is easily my favorite Zombie and I have won games off the back of its ability to hurt the opponent just by killing your creatures. If they don't have a way to disrupt you early and often, you can get out so many Zombies that at that point, sweeping the board is a tremendous liability. You can blow up the board yourself to finish off your opponents, or there's the fact that Plague Belcher is a 5/4 with menace before buffs.
