Zam Bie, king of the dead

All zombies you control have a +1/+1.
All zombies you control gain haste.
All zombies you control gain trample.
All zombies you control have, you may cast this creature from your graveyard as long as you
control a zombie.
When a creature you control dies amass 1.
When a creature your opponent controls dies
amass 1.
{x}{b}{u}{t}amass X.