Yorick, the Gravedigger

Whenever Yorick walks onto the field, spawn
4 mistwalkers that receive +1/+1 each. A
new mistwalker will spawn after an ally unit dies.
Sacrifice 4 creatures to summon the Maiden
of the Mist. This creature starts at +1/+2
and gains +1/+1 for everymistwalker on the field.