Phyrexian Dreadnought

Trample
When Phyrexian Dreadnought enters, sacrifice it unless you sacrifice any number of creatures with total power 12 or greater.

Reanimate

Put target creature card from a graveyard onto the battlefield under your control. You lose life equal to its mana value.

Target creature gets -1/-1 until end of turn.
Morbid — That creature gets -13/-13 until end of turn instead if a creature died this turn.

You have no maximum hand size.
{T}: Add {C}.

Search your library for a card, then shuffle and put that card on top. You lose 2 life.

Other Zombie creatures get +1/+1.
{1}{B}, {T}: Return target Zombie card from your graveyard to your hand.

{1}{B}, {T}, Discard a card: Create a 2/2 black Zombie creature token.
Tap three untapped Zombies you control: You draw a card and you lose 1 life.

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

As an additional cost to cast this spell, sacrifice a creature.
Draw two cards.

Gravecrawler can't block.
You may cast Gravecrawler from your graveyard as long as you control a Zombie.

As an additional cost to cast this spell, discard a card or pay 3 life.
Destroy target creature or planeswalker.

Sacrifice a creature: Add one mana of any color.

{B}, {T}, Sacrifice another creature: Create X 2/2 black Zombie creature tokens, where X is the sacrificed creature's power.