Commence the Endgame

This spell can't be countered.
Draw two cards, then amass Zombies X, where X is the number of cards in your hand. (Put X +1/+1 counters on an Army you control. It's also a Zombie. If you don't control an Army, create a 0/0 black Zombie Army creature token first.)

Ammit Eternal

Afflict 3 (Whenever this creature becomes blocked, defending player loses 3 life.)
Whenever an opponent casts a spell, put a -1/-1 counter on this creature.
Whenever this creature deals combat damage to a player, remove all -1/-1 counters from it.

Blighted Bat

Flying
{1}: This creature gains haste until end of turn.

Black Oak of Odunos

Defender
{B}, Tap another untapped creature you control: This creature gets +1/+1 until end of turn.

Grave Pact

Whenever a creature you control dies, each other player sacrifices a creature of their choice.

Aven Eternal

Flying
When this creature enters, amass Zombies 1. (Put a +1/+1 counter on an Army you control. It's also a Zombie. If you don't control an Army, create a 0/0 black Zombie Army creature token first.)

Finale of Eternity

Destroy up to three target creatures with toughness X or less. If X is 10 or more, return all creature cards from your graveyard to the battlefield.