Sideboard:
Rootborn Defenses – Side in if board wipes are very prevalent
Necromancer's Covenant - For graveyard-heavy metas. For the zombie lifelink to be relevant, I'm probably in very good shape already.

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Cards I might add:
Orzhov Cluestone, Worn Powerstone, Burnished Hart - More ramp
Yahenni, Undying Partisan - Free sac outlet, and a great play before a board wipe
Hour of Revelation - Cheap boardwipe that deals with things Teysa can't target
Carnival of Souls
Vish Kal - Another way to go infinite, but also just on theme
Elspeth, Knight-Errant - Amazing if I can get her to ult, but otherwise a token generator or a way to push through some damage
Lingering Souls - A cheap way to get a few tokens
Karlov of the Ghost Council
Angel of Sanctions
Wing Shards – Better than Swords to Plowshares vs Narset, but worse vs utility creatures that aren't attacking (e.g. Mayael)
Drogskol Cavalry - Token generator with built-in lifegain
Bygone Bishop - Possibly another Mentor of the Meek in this deck?
Black Market
Intangible Virtue
Caged Sun - Anthem and ramp to the really big turns
Darien, King of Kjeldor
Vedalken Orrery
Sram's Expertise
Call for Unity
Entrapment Maneuver
Collective Effort

Sacrifice package:
Ogre Slumlord - Rats, rats, rats. Not incredible when tokens are the main sac targets
Reassembling Skeleton/Nether Traitor/Ophiomancer - Main reusable sac targets
Viscera Seer - Free sac outlet that doesn't do much if it's not a bigger focus
Victimize, Sadistic Hypnotist - Sac outlets with big upside
Grave Pact, Butcher of Malakir - Additional copies of this effect
Maw of the Obzedat - Sac outlet and anthem. Sac blocked attackers to pump the others
Reprocess - Card draw
Grim Haruspex - Card draw with same downside as Slumlord

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Cards I might cut:
Requiem Angel – Very expensive for the effect that requires my dudes to die, but can be abused
Reliquary Tower - How much card draw do I have anyway?
White Sun's Zenith
Decree of Justice
Ravos, Soultender
Monastery Mentor
Luminarch Ascension - How easy is it to avoid this? Usually good on turn 2 but very hard later
Boseiju - Don't have THAT many instants and sorceries, and a tapped, colorless land that ALWAYS costs me life isn't great. I do have lots of stuff to offset the lifeloss, though

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Cuts:
Archon of Redemption - Not enough focus on fliers for this relatively small creature to be worthwhile
Angelic Skirmisher - None of these abilities are particularly impressive on tiny tokens, and when I have huge tokens I'm probably winning anyway
Bloodline Keeper - Too slow when I don't have more vampires
Myr Battlesphere - Basically a 7-mana "Put 4 1/1 tokens on the battlefield". Can be abused with a sac outlet (e.g. Blasting Station) and Karmic Guide or just Trading Post, though.
Skeletal Vampire - Can trigger "dies" triggers like Dictate of Erebos, Teysa or Requiem Angel, but the cost of the ability is very high
Soul sisters, Suture Priest - Too slow, too low impact
Thraben Doomsayer - Slow token producer, and if I'm at 5 health, the anthem probably doesn't matter
Nomads' Assembly - Win-more?
Carnage Altar - Too expensive to activate
Jar of Eyeballs - Probably too slow to be an efficient "tutor"
Sword of the Paruns - Just playing anthems is probably better to get power and toughness simultaneously. Moving this around is too expensive
Attrition - Should have enough spot removal with Teysa that I don't need this
Breeding Pit - Too slow to be worth the upkeep cost
First Response - Will prevent people from poking me, but doesn't do much against big attacks
Leyline of the Meek - Expensive anthem that only works on my tokens
Ajani, Caller of Pride - The ultimate is perfect, but getting there takes a long time of using a not-very-effective ability
Bloodgift Demon - Draws a card and provides a relatively big flying body, but doesn't otherwise do much for the deck
Erebos - Being an aggro deck, it's nice to prevent opponents from gaining life. Drawing cards is nice as well, but again, doesn't fit the theme
Swords to Plowshares - With Teysa's ability, we don't really need to use a card for exiling a single creature
Akroma's Vengeance - Replaced with Final Judgment which is better against creatures and leaves my enchantments/artifacts alone
Geist-Honored Monk – Only two additional tokens, and a big, non-evasive dude...
Increasing Ambition – Tutors? Hmm... Meh!
Vish Kal - I have Teysa for removal. Would rather use this in Karador
Whip of Erebos - I have so much other lifegain, and not enough creatures to whip back? Not sure, might need this.
Trading Post - Doesn't really do anything...
Mimic Vat - Being able to make some copies of good stuff with ETB abilities is nice (and I guess the copies are tokens), but this is a better fit elsewhere
Storm Herd - Too expensive
Rout - Don't really need all these boardwipes, and I have Teysa for instant speed removal
Final Judgment - Already have Teysa for exile
Emeria Angel - Low impact
Captain of the Watch - Lowering curve, and my tokens are more varied, so soldier-only anthem is kind of meh
Necropolis Regent - BBB can be quite hard, and if my tokens are connecting, I'm not sure I need this. Also curve
Sudden Spoiling - Doesn't really do anything specific for the deck
Empty the Pits - Quite expensive, BBBB is tough and not sure how on-theme it is
Decree of Pain - Quite expensive, and can only deal with creatures
Planar Cleansing - I want a board presence, and this doesn't spare any of my stuff
Deploy to the Front - Probably too expensive
Army of the Damned - Not so focused on zombies, and this is very expensive
Trading Post – Gives utility, but I might not have enough artifacts to justify it
Proper Burial – Life gain can be risky, and this does nothing else.
Mobilization - The vigilance is not very relevant, and 3 mana is a bit much for a 1/1 on the ground with no other effects
Path of Bravery - If I can attack with enough tokens for the lifegain to  be relevant, I probably don't need it, and +1/+1 isn't that relevant if I'm at 40+ life anyway
Marshal's Anthem - The reanimation could be quite relevant, but is quite expensive. The small anthem is a nice bonus
Dictate of Heliod - The flash is nice, but as just an anthem, I don't know if it's worth it
Entreat the Angels - Quite restrictive in when I can use it effectively
Soul of Theros - Too expensive to activate
Mikaeus, the Lunarch - Too slow
Spear of Heliod - I have so much other removal, and this anthem is otherwise pretty minor
Gideon's Phalanx - Expensive, and was mainly there for the indestructible, which is probably hard to get off by the time I need it
Drana, Liberator of Malakir - If she can repeatedly connect with the player and give any substantial gain, I'm probably winning anyway
Brimaz - His tokens usually just die in the combat anyway
True Conviction - Can potentially speed of the clock a lot, especially with Vizkopa Guildmage, but is expensive and doesn't do anything if I don't have threats
Righteous Confluence - Probably have enough other lifegain, and the tokens themselves aren't super impressive. Flexibility is nice, but sorcery speed hurts
Heliod, God of the Sun - Making tokens with him is pretty expensive, and tokens and black creatures don't activate him. Much better with True Conviction
Hour of Reckoning - I'm playing quite a few non-token creatures I want to keep around, and the other 6 boardwipes are probably better
Opal Palace - Don't really need Teysa to get big from this even if I could, and it's not very likely that I will get to that point anyway
Elspeth Tirel - I have so many other sources of lifegain that the + isn't very exciting, and I have lots of stuff I don't want to blow up with the ult. The -2 is enough for a Teysa exile, but don't know if it's worth the slot.
Mistveil Plains - I don't really have any ways to shuffle my deck, so the bottom is no better than the graveyard
Emeria - 7 plains is almost every plains in my deck, so getting this active is highly unlikely
Barren Moor - I need to get my actual swamp count up, so can't afford to run this probably
Kjeldoran Outpost - Sacrificing a land is a real drawback
Sacred Mesa - Too expensive to keep going, though it could be a strong lategame drop
Deathbringer Liege - Don't have that many multicolored spells, or black spells for that matter