Necroduality

Whenever a nontoken Zombie you control enters, create a token that's a copy of that creature.

Sol Ring

Wilhelt, the Rotcleaver

Whenever another Zombie you control dies, if it didn't have decayed, create a 2/2 black Zombie creature token with decayed. (It can't block. When it attacks, sacrifice it at end of combat.)
At the beginning of your end step, you may sacrifice a Zombie. If you do, draw a card.

Dimir Signet

Arcane Signet

{T}: Add one mana of any color in your commander's color identity.

Death Baron

Skeletons you control and other Zombies you control get +1/+1 and have deathtouch.

Undead Warchief

Zombie spells you cast cost {1} less to cast.
Zombie creatures you control get +2/+1.