Mietheim, City of the Dead

Mietheim enters the battlefield tapped.
{t}: {w} or {b}
{x}{x}{w}{b},{t}: Exile X elf and/or dwarf cards
from graveyards. For each card exiled this way,
create two 1/1 white and black spirit creature
tokens with flying.
Once home to a great unified city, now it stands as a
haunted tomb.